Fire Tv Kodi questions

I hate to ask y’all because it’s probably answered a billion times but here it is.

I bought a fire stick for my girlfriend so that when I go over we can use it to watch movies and shows. Mainly going to use it for Netflix and HBO but would like an add on that allows me to watch a bunch of movies not on those services. And movies still in the theatres.

I downloaded Kodi but can’t decipher all the info out there to determine what is the best add on. Or how to actually install it.

Can yall point me in the right direction.

Thanks