The Plugins tab unifies three sources (SpigotMC, Modrinth, PaperMC Hangar) behind one search box. Type what you need; results arrive in seconds.
Results are filtered automatically by your server's software and version: incompatible content never even makes the list, so no more crashes from version mismatches.
Click Install and the plugin lands in the right folder. For most plugins a restart is enough — the panel warns you when needed.
Externally distributed resources also appear with an 'external' badge and install the same way.