Reviewing intro material
I was able to quickly go through the initial lessons of the German course I'm taking. Now when I do practice sessions there's too much material that I don't know.
How can I go back and review the initial lessons I did, so I can take notes more carefully?
It seems my only options are to practice all the material I'm already supposed to have learned (there's too much I didn't learn properly) or learn more new things.
As you bring the crown level of a skill to five, you will get plenty of practice on those skills. Additionally, the types of questions change, becoming (in my mind) more difficult. If you still need practice after that, there's a practice button available.
This does not mean that you should bring a skill to five crowns before going on to the next skill. You might want to read the comments on this post discussing the way to traverse the tree: https://forum.duolingo.com/comment/30906134