At a 10,000 foot view (pedants will take offense) you should look to use multiprocessing for tasks which are CPU bound, and asyncio/threads (but really asyncio if you can) for problems which are IO-bound.

This is a massive simplification but most useful for a beginner.

Additionally, asyncio is not the same as multithreading, because typically asyncio is powered by a single-threaded event loop and use of a mechanism like select/kqueue/IOCP/epoll.