I've tried duolingo, but it's not for me. It just teaches you phrases and words, without teaching you the structure. I need grammar rules and lists of preposit

I've tried duolingo, but it's not for me. It just teaches you phrases and words, without teaching you the structure. I need grammar rules and lists of prepositions and verb endings. I need ten examples in a row where you change out a single word, to teach you how it changes the rest of the sentence. Duolingo is just random flashcards, claiming to be grouped into lessons. I can absolutely see it as a companion tool to a proper language course, but it's not sufficient in itself, at least not for me.