As for yasuo, he's hypermobile, one of the few champs that can completely nullify skills (without using an ult), gets through early game on a shield (which loads when he moves) and doubled crit. Gets to load an aoe knockup with his short cd q, either janna like as a tornado, or if he combos it with his dash it becomes an aoe knockup around his model.
Basically, he does it all if you can time well enough. You could have a shield in trades if you don't let it be baited out. You can wreck teamfights if you load and land your aoe knockup in time. You can block quite the amount of damage with your wall, if you can react well enough and read your opponents. Damage that might come in you could dodge with your dash (through opponents) which is on a near nonexistant cooldown. His ult locks down every opponent who is currently knocked up or back and deals damage, and has huge range, so that's your entrance into a teamfight.
On the other hand, playing against him, you can bait the shield with a small amount of damage after which the shield goes up for 2 sec after which it disappears. The cooldown of his wall is long, if it's wasted, any form of cc deadly. His dash and wall are his defense, otherwise the first 2 items are usually full offensive (shiv-IE). In teamfights, knockups and knockbacks get twice as important to worry about. It's not just that champ, but as well yasuo that's going to come with it. As said before, yasuo's has to get loaded (it's clear around his character model when it's up), and is a tad awkward.
Probably watch a couple of vids
His abilities just show he's got a lot of things to do when playing, and a couple of choices in that as well. You probably learn more seeing someone good use him than from reading a couple of guides.
