The top 3 in Matthew's chart are block-planes - used for small trimming tasks in joinery. Like most joinery planes you could use a chisel to do the same job, but sometimes it's more covenient to have a specialised plane, especially if it's for a task you do frequently. Plenty of folk reckon a good block plane is so useful that it's considered pretty much essential.
The rest are bench planes. Each good for making wood smaller, smoother and straighter to varying degrees. The longer planes get you straight and accurate. The shorter planes get you a luxurious smooth, silky finish. Mid size planes do a bit of both and are sometimes used for quick stock removal. If you do a lot of handtool work you'll probably want a few bench planes. If you're mixing hand tools and power tools you can get on with less.
A good compromise is a mid size plane like a #5 Jack. With mine I use a skinny off the shelf cutting iron and a thicker after-market chip breaker for coarse stock removal, then switch to a thicker after-market cutting iron paired with the skinny chip-breaker that came with the plane for getting pieces straight and accurate. Switching the irons that way means you can easily change the setup of the plane to be perfect for different jobs without having to do any finnicky adjustments.
There's no one-size-fits-all with planes. What you need depends on how you want to work and what sort of projects you want to undertake, but a #5 is often as good a place to start as any. Oh, and the clue's in the name as they say, but bench planes are best used in partnership with a bench.
