So I’m just a begginer and decided to start some Gauntlet runs today. What cards should I look for, what classes should I pick? (I guess Gauntlet works exactly like Arena in HS). Every help and tip will be appreciated 
Any Gauntlet tips?
Really pick what you are comfortable with, there are some Gauntlet guides over on http://managlow.com/ if you want to have a look
Here’s a link to Zelda’s gauntlet guide. I don’t know much myself about gauntlet, but this guide really helped me get a lot of value out of gauntlet. I highly advise you to check this out!
Seems I can’t open it
Nvm it’s on the page
http://managlow.com/how-much-does-synergy-matter-while-drafting-in-the-gauntlet/
there is also a link to it here
And is there any tierlist for cards?
The strongest faction in gautlet, according to the opinion of most people, is Abyssian (Lilithe specifically). Deathwatch synergy combined with Lilithe’s bloodborn spell is incredibly consistent and generally good; most factions lack the same level of consistency when it comes to making drafts.
I would recommend playing Lyonar (Argeon) and Vanar (Kara), They’re the most straightforward generals in my opinion.
I wouldn’t rely too heavily on Gauntlet lists. I think those exist, sort of like the Hearthstone arena tier lists. If you’re starting out Gauntlet is a good chance to try some cards you’ve never seen before. You’ll learn way more that way.
Best things to focus on is choosing a balanced mana curve. You want a curve that has a lot of 2 and 3 mana cards, some solid 4-mana & 5-mana cards, and just a few big cards that will hopefully finish the game for you. The basic path to victory in gauntlet is to use all your mana for the first 3-4 turns and win board control. That makes it a lot easier to do face damage in the mid-game and finish your opponent by about the 8 or 9 mana crystal turn.
In general favor minions that do something the turn you play them. Cards like primus fist, dancing blades, repulsor beast, primus shieldmaster and so on are premium.
Lastly, they aren’t flashy but don’t underestimate the power of basic minions with good stats. Hailstone Golem, Brightmoss Golem, and Stormmetal Golem are top notch for their stats and they can’t be silenced so your opponent has to deal with them. To a lesser extent Dragonbone Golem is ok but 7 mana can only be played in the late game and you can never accelerate into it with the mana orbs. A lot of times the game will end before you even get to play it. Any 2-mana minion with 2/3 stats is premium.
Noob cards to avoid are things like 2-drops with 3/2 stats, cards like Thorn Needler (only 4 HP for 4 mana), Bloodshard Golem (only 3 HP for 3 mana) because they are easily killed and they cost you a bunch of mana.