I just started playing this game and it seems pretty cool. Is there any advice you guys can give me?
Ex:
Whats overpowered?
What do a lot of people to repeatedly?
What character should i use for what?
Stuff like that.

Yes.

You have to play the game and see what it's like for yourself. Then maybe people can help you when you know what you're talking about.

"Overpowered" changes very often as decks/meta change to counter any "overpowered" decks that become popular. If you are new, you won't have any of the cards to make these so I wouldn't make this a concern.

What do you mean? Mistakes? How they play? This all depends on the decks you're facing. I would learn the terms aggro, midrange, tempo, control and combo.

Every deck can play every playstyle. Some better than others.

Honestly, I think you need to play the game for a week or 2, then come back with questions. It seems like you haven't done much yet.

I recommend watching "Trump's Teachings" - 2 hours well invested. He explains the basic strategies of the game and got an example for each lesson with different classes. He uses a mage for board control, a Shaman for favorable trading etc. and uses basic cards only (the ones you get if you reach level 10 with a class).
here's the link:
http://www.trumpfans.com/basic-decks/

I'm a low rank player myself and opened a thread yesterday which might help you a little, too:
http://forums.d2jsp.org/topic.php?t=73160619&f=221

I strongly recommend playing each class for a few games each and climb the ladder to rank 20 in each month for the reward (you can easily do that with basic cards only and never fall below rank 20, no matter how often you lose).
You should also win one Tavern brawl per week for the reward (one free card pack).

I found out that I do not enjoy playing Rogue myself and that I enjoy Hunter, Shaman, Paladin and Mage (just to call a few classes). It's unlikely that I suddenly play Rogue only after one Rogue build is seen overpowered in a new meta (well, I'm interested in a Pirate Rogue build, but that's another story ^^ ).
Going for the "one new overpowered deck" is quite expensive, too. There are current Control Warrior decks out there that cost more than 18k dust to craft - in the basic, non-golden version. Others played successfully 2500 dust Patron Warrior decks last month (pre-tournament).

This post was edited by Bunkerassel on Sep 2 2015 12:23am

1 tip for you, use some time to read these links.

http://lmgtfy.com/?q=hearthstone+tips+for+beginners

..and don't disenchant any cards what u get from packs until u familiar with them.

U can play what char u want, my opinion is that Rogue is most hard class to play at the beginning.