That works easily when you want to join communities already on your instance. But if you want to search for other communities you need to go to https://browse.feddit.de/, search for them there, copy the url, then join. Also you cant sort that list by anything, you kinda need to know what you are looking for.

Its....a bit too complicated. I'm sure it will get better with time.

Yeah. Joining communities from other instances is a hassle. Kinda puts me off sometimes.