If they are using exploits or cheats you can report them using infos you can find here:
If they’re totally blocking the server playability like blocking new players spawning area you can report them as stated here (you’ll need evidences, so take screenshots)
If they’re just blocking wide areas of the map… try anyway in the way I linked you, but being aware it’s a grey area. It’s supposed to be a unfair but “tolerated” strategy and on healthy servers other players should prevent or block guys doing this, but if they didn’t and nothing can be do now… well in the worst case change server.
If for any reason you’re unable to contact members of the community because as new user (oh sorry. welcome in the first place ) you may not be able to use private messages, first of all add a reply here using “@” and “community” to have them being notified, so they’ll can help you