I'm used to asking what is strong, what would be similar to what I like, etc. However, the answers I got didn't end up being as helpfull as I had hoped... So, i'll try a different way this time : What playstyle does sej fits? Or something like that. Sorry, I feel like my question is very vague.
zac probably, aoe cc ap tank also neither of them are banned with these last new patches out, so you're pretty safe from bans [slayer-pantheon-thumbs]
So you want to know how to better use Sejuani? I'm not following.
" I'm used to asking what is strong, what would be similar to what I like, etc. However, the answers I got didn't end up being as helpfull as I had hoped... "
Naturally. You ask a question like that, all people are going to hear is "Tell me who your favorite champion is! And talk them up for a bit if you would like." It's why the real answer to every Who to Play thread is to play the free weeks and buy the ones that you had fun playing.
"So, i'll try a different way this time : What playstyle does sej fits? Or something like that."
Tanky initiator. Does that explain it? 
She's supposed to deal more damage than your average tank (the tradeoff being that she has no real tank steroid, and they keep nerfing her damage because balance team, so idk). She scales off health, but season 5 frozen heart was still fantastic on her (dunno about s6). Her early clears suck and she can't solo dragon effectively (midgame she CAN but it'll take a week) but her ganks are pretty awesome. HUGE power spike at six; your laners should understand that unless the enemy is hugely overextending you're better off getting six asap.
Her job is to start a fight and then sit in the middle of it shitting out damage. Her problems start when you're on a team with noncommittal wimps. I like taking exhaust over flash because she can already get over most walls and more cc is always good, and if you find yourself needing to get out of bad engages a lot you're either making bad decisions or your team is worthless (in which case it makes no difference what you have). I find she's at her best when she's counterganking, so make sure you're warding and keeping on top of scuttles. Q breaks channels so if you've got an enemy MF, Nunu, or Kat make sure you save it in teamfights.
