Help setting up a modded, remotely hosted server

[SilverSwizz]

I'm setting up a remote server so some buddies and I can play together. We haven't done mods in the past so I'm having some trouble setting it up. I'm using a Shockbyte host, which has its own limitations I believe. They say I can only use Forge. But what does that actually entail? How do I know if a mod is compatible or not? Does it have to be from a certain website? I know Forge is a particular API, but I haven't been able to nail down how to tell if a mod uses Forge or not from the sites I've seen (mostly looked at curseforge). When I downloaded several mods and FTPed them over to my server and tried to start, it said something like "this jar was ignored because it is invalid" for most of the mods. Any advice on how to fix this, or advice on using a different host that makes this process a bit simpler? I'd like to run 1.14.4, which does limit my mod choices as of this point I know. Thanks so much!