How to install third party sound libraries?

So I'm incredibly naive when it comes to this type of stuff. I have all these sounds, samples, packs, etc. that I have downloaded but I don't know how to get them to appear in Logic. The best I can do is drag and drop but that only works on some files and it only works within that session, so I have to drag and drop again when I reopen the session. I tried following some tutorials but for some reason my sounds are always greyed out when it comes to that part of the video. I think what I'm trying to do it set up a sound library that Logic can access each time I open a session, right? Like for example on the school computers I can open Logic and use a plug in no problem, but on my own laptop I have it downloaded but it doesn't show up in Logic. Do I create a new folder to house all of the downloaded plug ins, sounds, etc. or does it automatically go somewhere and then I need to find it and link it with Logic. If so, can someone explain to me how to do that?

Sorry if this is a stupid question, like I said I'm pretty dumb when it comes to this stuff. Pretend you're explaining to someone who didn't have internet or electronics growing up.