the fastest way is to take lessons in immersion, a few hours every day (ideally 3-4), at least 6 months

The fastest way is to take lessons.

The fastest/easiest ways are mostly movies/shows and speaking with people.

if you speak very fast people won't understand you...

It depends on what you want to learn and how much of English you want to learn. If you want to learn how to pronounce a few words then sure it can be fast. But if you want to learn how to communicate clearly with native English speakers and become fluent, that takes time, effort and determination.