Very roughly, there are two main duties - bench planes and joinery (or specialist) planes. Bench planes are for the roughing down of sawn boards, truing them up flat and square, and smoothing off. Short ones tend to be smoothing planes, very long ones try and jointer planes (for truing up) and medium sized ones for roughing (jack planes), though there's a fair degree of overlap! They can be either metal bodied, wooden bodied, or a combination of the two.
Joinery planes tend to have specific functions, such as making grooves (plough planes), sinking rebates (rebate planes), levelling the bottoms of trenches and housings (router planes), truing tenon shoulders (shoulder planes) and such advanced stuff as making mouldings. Again, both metal bodied and wooden bodied examples of most exist.
There are all sorts of variations, oddities, specialist planes, home-made dodges and lash-ups, historical anomalies and so on which you'll no doubt come across as time goes on, too.
Generally speaking, some planes of a type are better than others (just like everything else in life), but you don't always need 'the best' to do decent work. You do, however, need some knowledge of how to use and maintain them to do decent work, so some research into planing technique is just as important as research into planes.
A good book for the outright beginner is Robert Wearing's 'The Essential Woodworker', available either second-hand (if you can find a copy at a reasonable price) or new from Classic Hand Tools;
https://www.classichandtools.com/acatal ... l#SID=1220
