http://champion.gg/ states that in the highest elos Leblanc and Yasuo have some of the lower end winrates (sub 50 percent by decent margins)
Generally Leblanc is a /good/ champion. She dominates the early stages of the game where someone is forced to be near her at all times. If they are too afraid to pressure her she just gets kills from other people due to spectacular roam potential. Leblanc's damage onto a single target is both fast and so high it's nearly unfair while remaining relatively simple to perform on. The weaknesses she shows are heavy though - clearing waves requires you to pop long cooldowns attached to high mana costs, and even when you do that the minions will usually struggle through on slivers of health requiring you to auto attack them to finish them. This means she's countered by people who clear waves quickly and safely (Azir is an example, his solders extend his range so that Leblanc can't quite reach him, but they provide him the AOE necessary to clear minions away). Overall Leblanc isn't the worst pickup you could have and one of my very unskilled friends plays her the most out of all the champs
Yasuo is tricky from a player perspective. Especially for a new player, actually unlocking everything Yasuo can do is really difficult. The longer you play League in general the easier it is to pick up new champions, but assuming you're new to it Yasuo will not be simple to play effectively. Yasuo's power is so gated by his inherent weaknesses (poor base stats like health and damage) that even experienced players falter when playing him (that's why his winrate is so low). Overall he's a champion known for his "big flashy plays" and a lot of people find him to be extremely fun. Most Yasuo players are fairly dedicated because of this and ignore many of the other champions as well as many of the game's core mechanics (they will do things they shouldn't because they get caught up in the blistering pace of Yasuo) He's generally countered by tank champions (especially when he has to lane against them like in top lane) because he can't deal enough damage to get them to back away from him. He's strong against champions with projectiles (especially ADC's) because his W blocks them. As an assassin he'll blow up targets with less defensive stats as he gets to them, so he can remove higher priority targets from the fighting
Yasuo does Physical damage, Leblanc does Magic damage. Let me know if anything needs clarifying (I don't know how inexperienced you are? What's your account name?)