Global Members are members in the global namespace, and can be used anywhere.
A full list can be found here:
Properties[]
game: DataModel []
A reference to the game's DataModel.
workspce: Workspace []
A reference to the game's 
Workspace.
_G: array[]
An array that can be used in any code in any script. This array is different on server/client.
Methods[]
UserSettings(): UserSettings[]
Returns the local player's UserSettings
assert(v: Variant, error: string = ""): void[]
Throws an error if the given 'v' is false or nil. If no error is given, it will throw "assertion failed!"
collectgarbage(option: string): Variant[]
Collects garbage based on the given option. The only available option is "count". If count, it will return the amount of memory in use by Lua, in Kbytes.
error(message: string, level: int = 1): void[]
Causes a standard Lua error, with the message being message.