I have zero formal musical training but I have managed to become reasonably proficient (D level) at 3 chord rock and blues on guitar and bass. I know one scale (pentatonic, ok so maybe that's 2 scales Pentatonic minor and Pentatonic major!). But I have learned enough that I can play and write songs. If you want to make music, especially with others, it is useful to understand the basics of musical language, like chords, keys, what I-IV-V means, etc. But the concepts are not that hard.