Most F-Droid stuff AFAIK should be pretty plug and play. It'll download an APK which you then just open in order to install the app. You may need a file browser app if your phone OS doesn't come with one. You may also need to allow installs from third party somewhere in the settings. But android isn't like iOS and won't generally restrict your ability to install whatever you want, outside of an options popup to make sure you know what you're doing.
I don't use LibreTube personally and can't speak on that specifically though, if it does something other than just download you an APK file.
I had a look at VaatiVidya's video on this (many spoilers, you are warned) and while this all looks incredibly awesome, all I can think about seeing some of the new weapons are how these things are going to be an absolute menace in PvP. Specifically the >!beast claws.!<
Good thing I'm already trash at PvP and am used to losing, because it looks like we're getting like 8 new variations on what made Rivers of Blood a meta pick. I'm not really that upset about it, PvP isn't my main draw to elden ring and I am going to have a ton of fun with these new weapons in single player, so I consider it a net positive, but even so, yeesh.