FM = Frequency Modulation. Some scanners have a wide & a narrow mode. On a scanner the wide mode is for Broadcast Radio & the Narrow is for everything else. (VHF/UHF trancivers may use Wide for amateur radio & Narrow for PMR)
Most analogue VHF/UHF voice transmissions are FM. It is clearer that AM in general.
AM= Amplitude Modulation. Airband is AM. AM is in terms of VHF/UHF the old fashioned mode, it is a carrier with a top & a bottom side band both containing the audio.
SSB= An AM signal minus it's carrier & with only one of the audio streams transmitted, that being the Upper or Lower Side Band. On Amateur radio the convention is to use the Lower Side Band (LSB) below 10 MHz & the Upper Side Band (USB) above 10 mhz. It is possible to hear FM on an AM radio & AM on a FM radio, even if the audio is not as clear as it should be. However SSB cannot be heard on a FM radio, but there are ways to "resolve" the audio using a pair of AM radios, although that does require some experience. In general the right kind of radio or an extra box is really needed to listen to more than an occasional SSB signal.
SSB is a much narrower signal that AM or FM & it sounds very different, so it takes most people some time to get use to it's sound, to hear it properly & it also takes time to properly tune it in, so it is not a Scanner mode.
The above are the main modes. Others include.
CW (Continuous Wave) also known as Morse Code as CW is turned on & off in short or long busts to produce dit's & dah's, thus producing a language.
SSTV, Slow Scan TV. This slowly builds up a image on a screen, line by line.
RTTY, Radio Teletype, this is now an old fashioned mode & not as widely used as it was in the 70's & 80's.
ATV, Amateur TV. Normally high quality TV signals.
PSK, a reasonably new digital mode, that is comparatively simple to send & receive. A sound card & freeware is all that is really needed.
IRLP, Internet Radio Linking Protocol. This is simply linking radios via repeaters & the internet. Can be used on 446, Amateur radio etc etc.
Various digital voice modes. Many of these are based on FM. Like other voice modes they require the right kind of receiver or an extra box, (PC in this case) to resolve the audio. And like other modes, digital can either be encoded or un encoded. So some Tetra (Terrestrial Trunked Radio) users as an example are encoded, while others are not.
Trunked Radio. In effect a method of using spectrum more efficiently. It allows a number of different users or members of the same talk group, to use the same small lump of spectrum differently.
Conventional AM/FM assigns a frequency. Trunked Radio is in effect a network of channels, that are used dynamically, so there is no exact setting for any single user or any single QSO.