Dr. Stephen Krashen is a great teacher and researcher of Second Language Acquisition. He explains the difference between learning languages versus language acquisition very well.
When we learn a language, think about all of those rote things that you do. Flashcards and apps, exercises, going to a traditional language class, studying verbs, or going to a language lab. Those are all traditional, deliberate activities to learn a new language. They work by helping you get new patterns and words into your long-term memory that eventually all work together to a level where you can create your own language and sentences.
Acquisition is something that’s slightly different. Acquisition is the way that you learned your first language. You were spoken to, you watched TV, you were read to, you went to school, or you listened to music, to name just a few ways we acquire language. You were completely immersed in that language. Instead of learning separate words and phrases, or verb tenses and patterns, in the way we talked about with learning, you absorbed all the messages you heard and read naturally.
Many people who learn multiple languages, and/or learn languages to very high levels, understand how these two things work together. You want to be deliberate in your studies, journaling, use of flashcards, regular chunks of time to study and study of grammar. In combination with regular, focused periods of study, you also want to spend a lot of time in acquisition. This could be speaking to native speakers, traveling, reading, watching movies or listening to music. Again, those immersive activities that taught you your own language. You will make swift progress when you learn how to combine these two things.