Students often ask me questions like: "Can you explain phrasal verbs?" or "Can you explain how to use prepositions?"
The problem is that the word explain implies that phrasal verbs and prepositions are grammar issues with easy rules. In fact, there are no easy rules to explain phrasal verbs, prepositions, and many other areas of language. Instead of treating these things as relating to grammar, it's best to see them as vocabulary items.
In any language, some things can be explained using grammar rules. Unfortunately, everything else is vocabulary. You don't need to explain vocabulary; you just need to learn it gradually.