How do I assign hotkeys?

I want to make a hotkey for opening your inventory, for example if you press "E" it will open your inventory GUI. How do you do that?

Please make an effort by Googling what you want to do and searching the wiki before posting here

You can use ContextActionService or UserInputService to register key presses.

ContextActionService:

http://wiki.roblox.com/index.php?title=API:Class/ContextActionService

http://wiki.roblox.com/index.php?title=ContextActionService_Tutorial

UserInputService:

http://wiki.roblox.com/index.php?title=API:Class/UserInputService

I would recommend ContextActionService if you are planning on having cross-platform support.