Grammar tips and notes
These are really really helpful, but some of them are honestly not done that well. Things like what inflection means, or imperative moods aren't explained and it's really hard to follow what exactly it's talking about. (I didn't know where else to post this lol)
The grammar tips and notes are very limited. They are here just to facilitate your learning on Duolingo, not to be your only learning material. Learning only with Duolingo won't get you very far, but it can be a very useful "jumping board" towards additional resources. And especially for the two languages you are learning, German and Spanish, internet is full of excellent resources that you can use.