Hey, folks, you’re going OT. The OP asked *how* to learn Yiddish, not *whether* to learn Yiddish.
I agree with RebRY – you need to be around people who speak it, and speak it yourself. That’s how I did it. I found someone to speak Yiddish with me – I would visit them once a week and speak Yiddish (I really broke my teeth).
You may find it easier to speak with children. Their speech is simpler and I found myself less self-concious than with an adult.