By this I mean can you access localplayer from CoreGui? Is CoreGui on the client or on the server?
I'm wondering this because I'm trying to put a GUI inside of the player but whenever I put it in CoreGui it doesn't work. Does anyone know if it works on the clients or servers side?
It's local.
It's a GUI thing, the server doesn't render GUIs, therefore it's purely logical that it would be a client-only thing. Also put GUIs inside of the PlayerGui, you're not supposed to touch CoreGui.
Server, It's on roblox. CoreGui is for client only. In summary, on server, for client.
Read more here. http://wiki.roblox.com/index.php?title=API:Class/CoreGui