I've been playin yasuo mid in silver V and do pretty bad. people tell me not to play yasuo in low elo and there are also videos saying other champions are better for low elo. i just want to know, why do some champions do better in low elo than the rest? also, tell me some good champs for elo, too. is master yi a good one?
Because if you're in low elo chances are you're not amazing at such a high mechanical champ, it's why people don't recommend you play zed in bronze because if you're bronze, unless you're a god zed chances are you can't handle his difficultly on a gold scale level. Not pointing fingers at you particularly, but just the general idea of why "don't play champ x in low elo".
Another issue is some champs require too much team coordination and understanding of how you work, so a bronze might not follow or keep up with you easily. Yasuo for example, the team might not engage when you ult or the team won't build a comp around you (one major flaw with yas is he makes the team have to lock in with what works for him.). I one tricked elise through bronze to get where I am, and it was hell to get out because people didn't know how my rappel mechanic worked and would run out mid dive, in high silver I notice people are much more commited to it, that or people didn't know how to build for the late game with how I fall off.
You can climb with any champ, you just gotta be extremely good at them inorder to have the best success.
because some champions are hard to play and therefore not recommended for low elo.
Such as 
and so on..
Yes, 
is a good champion for beginners as he is easy to play.
HF and enjoy your free Pentas :)
You want to avoid champions that rely on team coordination to work and focus on ones that require enemy team coordination to stop. That's why someone like Yas who greatly relies on teammates for good ultimates won't work while with, say, Katarina you can carry much more easily if they don't save CC for you.
Generally, simpler champions are better at low ELO. More complex champions are balanced around players using them near their skill-cap and low-ELO players just aren't good enough at them to overshadow other picks.
If you are looking for champions who would be good in low ELO, I'd recommend picking champions with some of the following quantities:
You can often get away with some odd picks in low-ELO that wouldn't work well in high ELO play since people will often not know or be able to implement the apprioriate counter-play against them.
Also, you would be surprised how many people try to claim that CC isn't a counter against Master Yi or Katarina because "CC affects every champion".
Want some champs here ya go. Top: Maokai, malphite, chogath, trudle Jungle: amumu, volibear, sej Mid: lux, annie, malz Ad: ezreal, caitlyn, ashe Support: Blitz, soraka, braum
Tanks are bad in low elo because they rely on team coordination, other than that I think any is fine.
Easy to use kits w/ few skill shots/combos...
Oh, and higher elo it appears that utility spells out play damage spells..
Because champions have different strengths and weaknesses; playing well means working to those strengths and diminishing the weaknesses. Some champions haves strengths that are harder to work towards, that are less obvious, or have harder to patch weaknesses. Or even have exploitable things about them or in the match. That's why some champions can be considered better for low elo than others.
People say that some champions should not be played in low elo because they have personal lists of how "easy" champions are, based on their personal impressions (and whether or not they play that champion) and will tell people not to play the "hard" ones. Likely, that's what those people you were talking to were saying.
