Nice question :) A good textbook should go over the sounds in the language comparing them to something in the target audience's language. This isn't foolproof (a language YouTuber (Language Jones, I think?) was talking about trying to learn an African language, but the author expected reader to speak South African English where vowels differ from, for instance, US English), but it generally works pretty well. These days, wikipedia is also typically a great resource for reading about sounds in the language. Further, nowadays, you can toss stuff in Google Translate and have it speak. Finally, consume media from that country. When I was learning German, DeutscheWelle had a German-learning mp3 series. Also streaming radio in those days (no Youtube or anything yet).

Edit: and for output, the time-tested technique of shadowing is great. Record yourself if you can because your ears might do better picking up any mistakes when not speaking at the same time.