I always use an audio loudspeaker as an easier to understand comparison. If you look at a loudspeaker, it's job is to turn electrical energy in compression waves that travel through the air to our ears, where these changes in pressure get converted back to electricity that our brain 'decodes' as sound. Dangling a loudspeakers on it's two wires naked works pretty badly. A number of things are happening - the physical back and forth needs to couple to the air. Imagine the speaker is a big one, like on the parcel shelf of teenagers cars. as it kicks forwards, the air resists, and the actual speaker on it's dangly wires actually moves the other way, then the cone reverses, and the speaker gets pulled back the other way - net result very little sound from even quite big movements of the cone with plenty of power. This of course is low frequency operation. If that same speaker is fed with higher frequencies, then the physics of moving the entire heavy loudspeaker works for you (momentum and inertia, in this case), and more of the speaker movement makes it into the air, being carried to the ears. however, as a quality loudspeaker it's still pretty hopeless - it's inefficient because some of the energy going forwards gets counteracted by the rear of the cone - which is working in reverse. So this could be a cheap speaker or an expensive one - it has nothing to work against - so as a speaker is pretty poor. However, if you stick it in a box, the contains the reverse side of the cone, it dramatically gets better. The design of the box could have a total seal, or a speaker port - the difference is in how well that loudspeaker, in it's box handles the low frequencies through to the highs. The internal volume of the box impacts on the frequency response, and the efficiency. Suddenly that useless loudspeaker driver works much, much better.
This broadly aligns with how aerials work, but we do have to make sure the basics are understood. Dipole, for instance. The basic definition is something that has the capability to hold two opposing electric charges. So the usual device we thing of has the end of the coax feeder taken in two separate directions, extending from that point. That is a dipole. A half-wave dipole is just a description of a popular type that has a length determined by the frequency we wish to use. The half-wave measured from tip to tip - the longest it can be. A quarter wave dipole is the bit from the middle to one of the tips. If instead of another piece of wire, we plant the quarter wave element rising upwards from the roof of say a car, the car roof becomes the magically spoken about ground plane. A surface the quarter wave element can use to work against, instead of the missing other quarter wave element. In a way it becomes that element - but with it's surface area stretching to infinity. In the real world we can't get that big, but when it's biggish - it works much like that missing other element. It's related to frequency. So a UHF quarter wave rising from a car roof is pretty efficient - length against surface area. Move to CB frequencies, and that surface area (the ground plane) is really a bit small - hence why CB aerials are less efficient on a car. Stick one on a boat on the sea, and that surface area is much, much larger, and the aerial works an awful lot better.
When you use a simple half wave dipole - it's balanced. Each side of the thing is the same. The quarter wave on the car roof is unbalanced the two parts of the aerial being very different. For what its worth, ordinary coax cable is not balanced. There's a thin conductor in the middle, surrounded by a 'tube' of another conductor - not at all balanced, and it makes a good match with an unbalanced aerial system. If you want to connect a balanced aerial to an unbalanced feeder - you need the balun - simply a device to convert balanced to unbalance and vice-versa. A good one is almost transparent to the RF, while a bad one loses some of what you send through it.
We can use loudspeakers again to show what happens with aerials with gain. The typical small hi-fi loudspeaker gives listeners in the room pretty good sound no matter where they sit. They're a bit louder in front than behind, but the change is gentle. Compare these to those old fashioned how type speakers you still see at outside events. The speaker sits at the entrance to a trumpet like horn. This focusses the sound so that it gets directed in one direction. Imagine a loudspeaker as something rather like a globe, floating in space. The entire surface of the globe producing sound. Now imagine you have wrapped amazing soundproof material all around it except for the UK. None of that sound can escape anywhere apart from our little island. ALL the sound has to come out this way, in a beam. This is what those horn speakers are doing. Their design is also limited in frequency - hence why these horn speakers are great for speech and rubbish for music. One of these things might only handle a small amount of power from the PA system, but throws it a very long way.
PA systems for outside festivals have worked in this way for a long time now to appease the noise police. You want it loud where the people are, and quiet everywhere else. They are beams - working a bit like torches. Walk outside their design angles and the sound drops very quickly.
Sound and RF energy can reflect of things. They can also scatter it to places you don't want.
Most of this analogy works pretty well. There are differences of course that it's a bit too simple for, but in general terms, the similarities are quite surprising.
It also explains how many other radio systems work. The old pirate stations in the north sea - a huge tower that is actually the aerial - perched on top of a mass of salty water stretching for miles. It is the same as the quarter wave on the car roof. Salty water works even better than fresh. So remember that lattice towers may not be simply supporting aerials but could be the aerial itself.
All the talk of earths and grounds confuses people. Electrically, we kind of thing of earthing as safety based and something hurried in the ground - which of course it is. Radio wise - earthing can work for you, or against you depending on what you want to do. It's not good or bad, its more to do with what your aerial system needs to be efficient. If you had a huge tree in your garden, you could arrange for your feeder cable to emerge in the middle of the garden, and then be pulled up vertically towards the supporting tree branches. At the bottom, you bang in a nice metal rod, and connect to the cable screen. Your garden - wet soil mainly - becomes the 'sea' in my pirate example above. Not as good as salty water of course. but in the winter - pretty close. In the summer, with hardly any moisture in the soil, then not so good. Depending on your tree height you could have a nice quarter wave vertical for loads of bands, and quarter waves are pretty efficient aerials. You could even have 3/4 or 5/8 vertical elements and get a bit of extra performance from the gain these provide.
On the subject of gain - and again with some simplification we're doing two things. We have a longer active part of an aerial, on the principle that the more RF we get into the air, the better it is, but the actual aerial (remember the idea of it have electric charge) can work differently. If a bit of it is pushing while the other part is pulling (like the speaker) some cancellation can take place. It can also work for you and the two properties add up, so pushing, then a bit more pushing. The aerial design can also change how the RF leaves the aerial, direction wise. Remember the globe example again). Ig half of your signal goes upwards, and nobody is in that direction apart from the space station, if you can take this wasted energy and stuff it in the wanted direction you have created gain. It's not magic, this gain idea. You cannot increase the energy 'in' the aerial - all you can do is arrange for it to escape in useful direction and make better use of it.
There you go - my as non-technical as I can do attempt at explaining how these things we take for granted work.
Just keep in mind the basic principles - when you get to study it, you'll find many examples of much stranger things, some contradicting the above, but the basic ideas and physics are sound.
Maybe this will help get the basics sorted for beginners, as it does explain what appears to happen.