What's Forge?
Forge is the original Minecraft mod loader and still has the biggest library of mods. Most of the classic mods you've heard of (Create, Applied Energistics, Tinkers' Construct) are Forge mods. It's been around since 2011 and isn't going anywhere.
Setting up Forge
Click the + button in GDLauncher to create a new instance. Pick your Minecraft version and choose Forge as the mod loader. GDLauncher shows available Forge versions for that Minecraft version. The "recommended" one is usually the safest bet.
Give it a name and create. GDLauncher downloads Minecraft, Forge, and the right Java version automatically. You're ready to add mods.
Adding mods
Open your instance and go to the Addons tab. Click Add Addons to browse CurseForge and Modrinth together. Search for what you want, click Download, and you're set.
When looking at mods, make sure they're for Forge (not Fabric) and match your Minecraft version. Most mod pages make this clear.
Forge vs other loaders
Forge has the largest mod selection, especially for tech and magic mods. Fabric is lighter and updates faster for new Minecraft versions. NeoForge is a modern Forge fork with active development. Quilt runs most Fabric mods plus some extras.
Your choice depends on which mods you want to play. Check if the mod you want is on Forge or Fabric before picking a loader.
Troubleshooting
Forge not starting? Make sure you have at least 4GB of RAM allocated (more for modpacks). Try a different Forge version if one specific version has issues. Remove any recently added mods to check for conflicts.
Mods not working together? Verify all your mods are for the same Minecraft version and the same Forge version. Check mod pages for known incompatibilities or required dependencies. Some mods need library mods to function.
Popular Forge mods
Some good starting points: JEI (Just Enough Items) for recipe viewing, Create for mechanical contraptions, Applied Energistics 2 for digital storage, Tinkers' Construct for custom tools, and Biomes O' Plenty for new world generation.