“Server with mods” are three different things, and what you need to install depends on the type:
- server with its own launcher - install the server launcher, and it downloads all the mods and logs in;
- server with mod collection on Forge, NeoForge or Fabric - install the same modpack of the same version and go;
- server with plugins on Paper or Purpur - you don’t need to install anything: go with the regular game, and new items and modes are added by plugins on the server.
However, mods that change only the image and convenience — Sodium, Shaders, minicards — can be placed on almost any server: the server does not need them.