Prepositions can be very tricky, and it just takes a lot of time and exposure to get even close to feeling like you have them under control ! (This holds true for native English speakers learning French prepositions, and for native French speakers trying to understand English prepositions).

Suggest starting in Grammar Lessons/A1/prepositions and conjunctions - there are several lessons on different situations in which dans/en/à and other prepositions are used.

CEFR A1

The most important mistake to avoid is to start translating prepositions literally. Forget that à, dans, and en can all mean "in". That isn't helpful and will only confuse you. Start thinking like the French. Accept them as they are and allow yourself to develop a feel for them. Translating literally is just going to slow this process down.