Rosetta Stone is decent pedagogy.

There's no magic to learning language; it's something that humans do.

You need exposure to the language; "comprehensible input" is a nice googleable term

When you learned your first language, you had a caregiver who talked to you as you learned what was what. If you had that again in another language, you could gain proficiency, but that level of input is hard to fit into a normal life.