How do you learn new word/phrase?

Soon after listening to British English, I've been fond of learning English.
For me, talk or narration in English sound like music or poem whatever the theme is.

I don't know why. But I've been quite enthusiastic about learning English.

Apart from my enthusiasm, I'd like to ask tadokists the question in the title.

Sadly, my approach to learning English hasn't been so helpful that I've changed the way of learning it a few times, which haven't worked either.

Why can I use certain words or phrases very easily, while it's so difficult for me to use other words or phrases?

What do you think?