A longer response, as I hadn’t spotted neprostoman’s pithier version until just now and I’d already typed it

But basically, what neprostoman said!
First, by far the most important factor in whether you win or lose fights will be your tactics. Weapons and armour do matter, but not nearly as much at this stage.
- Is it better to use an 2 handed weappon, or sword and shild... I read somthing about "neet to learn first"
Either is fine, and it depends what you enjoy. You’ll have better defence with a shield but do more damage with a two handed weapon. So if you’re using a two handed weapon you might get damaged more, and therefore need to pay more attention to constitution, dexterity and armour (all of which can help you stay alive in different ways) but you’ll also potentially finish off your enemies more quickly so they have fewer turns to damage you. If you’re sticking with your barbarian, two handed is the classic choice as you have the HP and rage damage reduction to soak up hits and can concentrate on damage.
Some classes have abilities that give them some advantages when using a particular style of weapon, like Lae’zel with two handed weapons, so look out for that and you can choose weapons that make use of those abilities, though it’s not essential.
And you can only use weapons you are proficient in, which will depend on your race and class, but the game will look after that for you by preventing you equipping a weapon you can’t use.
When you level up to level 4 (the highest in early access) you can take one of a number of feats, one of which lets you learn a number of new weapon proficiencies, but that’s unlikely to be the best option for many, if any, characters. As a barbarian, you start out with lots of weapon proficiencies already, along with shields and medium and light armour.
- Shoult I gave my mage a bow?
Yes, give your mage a crossbow. Chances are they’ll be able to do more reliable single target damage with it than their cantrips after they run out of spell slots. But don’t ignore cantrips, as these can, eg, set barrels and surfaces on fire and because they don’t cost spell slots you can use them every turn.
- Shoult I buy a light armor or heavy if my partymember have not learn this. How can I learn this heavy armor? Automaticly by using?
You can only learn new armour proficiencies by using that feat I mentioned at level 4. I wouldn’t bother, as most of the time there will be a more useful feat. There’s not much heavy armour in early access anyway, and its armour class isn’t significantly better than the best medium armour, particularly if you have a dexterity bonus.
- How far astarion can walk to have enough points to use his dagger?
You get (1) an action, (2) a bonus action, and (3) movement you can use each turn. (And a reaction, but we’ll ignore that for now.) You can move the maximum distance possible and still use your main action to attack as well as your bonus action. There are some complexities with actions that use movement, but attack isn’t one of them.
All your party can also “Dash” as an action, which will let you move further, but you then won’t be able to use your main hand attack as you’ve already used your action for the turn.
Because Astarion is a rogue, you can instead use his special “cunning action” Dash which is a bonus action, and if you do that then he can move further and still attack with his main hand as an action.
If you give him another dagger (or, even better, short sword) for his other hand then he can attack with either his main action or bonus action, or both.
And if you choose the “Thief” subclass for him at level three, then he’ll get a second bonus action each turn, that he can use for another off hand attack or to dash or hide.
EDIT: By the way, if you stick with your barbarian, you’ll also get to choose a subclass for them at level three.
- Why the enemies can use 2 attacks sometimes and I only one?
There can be various reasons for this. In early access, it’s generally because they have a weapon in each hand so are attacking with both their action and bonus action. A small number of enemies might be hasted (you’ll find potions of speed in your travels) which temporarily gives two actions a turn. And some creatures have a multi-attack main action that gives them more than one hit.
Found some scrolls, should I use them or sell.
Money isn’t particularly scarce in this game, so I usually hang onto scrolls just in case I need them, and end up with them still in my inventory at the end! Be aware, though, that a wizard like Gale can copy scrolls to his spell book for a bit of gold if he doesn’t already know the spell. He can then memorise and use the spell.
Whats the difference between trade and exchange in the shop? (I'm not sure if my translation of "tauschen und handeln" is correct)
I think they’re described as trade and barter in the English language version. Trade just buys or sells for the recommended amount when you move items between your inventory and the merchant’s. Whereas barter lets you give items to merchants for less than they are worth to raise attitude, or just see everything you’re selling before you finalise the deal, and I think maybe only barter lets you sell everything in a character’s inventory you’ve marked as “Wares” at once. But I could be wrong there. I always just use the barter screen.
Hope that helps!
Good luck with your game.