Minecraft → Modpacks installs a whole pack at once: the right Minecraft version, the right loader version, and every mod in it.
- Open your server in the panel and go to Minecraft → Modpacks.
- Search for the pack. Packs come from Modrinth.
- Pick the pack version that matches what your players have installed.
- Install. The server is stopped first (and backed up, if it has backup space), and every file is checked as it's downloaded.
- Start the server when it's done.
Mods that only run on your PC
Packs often include client-only mods. They're left out of the server for you, because Modrinth packs mark which mods are client-only.
CurseForge packs
The tab doesn't install CurseForge packs. Many CurseForge authors only allow their files to be downloaded through the CurseForge app. If the pack is also on Modrinth, use that. If it isn't, download the pack's server files from CurseForge, check which Minecraft and loader versions it needs, set the server to that version, and upload the files over SFTP.
The pack needs a different loader
A pack built for Fabric won't run on a NeoForge server. The loader is fixed by the server type, so create a server of the type the pack needs.