Forge or NeoForge
Your pack decides, not you
NeoForge is a fork of Forge started in 2023, and many newer packs target it. The pack page states which loader it needs; that is the answer. Installing a pack through the Modpacks tool removes the question entirely, because it reads the manifest and installs the exact loader build the pack pins.
Use the Modpacks tab
When you want a published pack. It resolves the pack from Modrinth, installs the loader build it expects, skips client-only files and applies the pack’s server overrides. It is a clean install and replaces the current world, so back up first.
Use the Versions tab
When you want a bare Forge or NeoForge server to build up yourself. Pick the Minecraft version, and add mods afterwards from the Plugins tab or by uploading jars.