What you'll find
The folder you land in is the instance root. Inside, two layers: a top-level logs/ for the launcher's per-instance session logs, and an instance/ subfolder which is Minecraft's actual game directory. See Anatomy of an Instance Folder for the full layout.
The directory most people are looking for is instance/saves/ (worlds), instance/screenshots/ (screenshots taken with F2), or instance/config/ (mod config files).
What you can safely change
- Worlds: copy folders out for backup or in to import a downloaded world.
- Screenshots: pure assets, copy out as you like.
- Mod configs: edit
config/<modid>.tomlby hand, most mods reload changes on next launch. - options.txt: Minecraft's client settings. Editable as plain text.
- Resource packs / shader packs: drag in or out by hand if you'd rather not use the Addons tab.
What you should avoid changing
- level.dat inside a world: it's NBT-encoded; corrupting it kills the world.
- Region files in a world's
region/: same, NBT binary, edit only with proper tools (NBTExplorer, MCEdit). - Mod JARs in
instance/mods/if the instance is a locked modpack: the launcher won't know about manual changes and there'll be inconsistencies in the Addons tab.
Useful subfolders at a glance
instance/saves/, your Minecraft worlds.instance/screenshots/, in-game F2 screenshots.instance/mods/, the mod JARs.instance/config/, mod settings.instance/resourcepacks/, resource packs.instance/shaderpacks/, shader packs.instance/datapacks/, global data packs.instance/logs/, Minecraft's session logs (game side).instance/crash-reports/, Minecraft crash dumps.logs/(one level up), GDLauncher's session logs.
When the launcher is running
You can browse the instance folder while GDLauncher is running and even while Minecraft is running. Editing config files mid-session is fine for most mods (they reload on relaunch). Don't edit world files (level.dat, region files) while Minecraft has the world open, you'll cause corruption.