You're still *super* early in the game. At this stage just progress through the campaign and level up your champs.

Galek is unfortunately the worst starter of the set, and you are early enough that you may want to consider simply restarting and taking one of the other three.

If not, your first objective should be to get Galek to level 60.

https://ayumilove.net/raid-shadow-legends-guide/#do-and-dont is a good reference btw

You should go watch beginner guides on youtube to be honest. That will fill in the gap. Main goal for you now is getting your first level 60 champ. But there is a lot to do before that stage