Not a terribly helpful answer. I'm not sure I 100% understand it, but I'll give you what I think I know.

Pools assign work units, similar to the current block being worked on, however at difficulty 1 (or higher depending on your hashing power), which are called shares. The idea is that you solve your mini-block, and submit it back to the pool, to show your proof of work, out of every X shares submitted, one will also solve the "real" block being worked on (by chance).

So you are in essence solving an easier problem, that can potentially solve a more difficult one, and everyone doing this over and over and over eventually do find a block.