I am now inside my game. How do I bring up the overlay?
When XSplit Gamecaster loads into your game, you will see a notification that tells you what hot key is set to open the overlay.
The default hot key combination to show the XSplit Gamecaster overlay is CTRL-TAB. If you wish to change this, then go to the hot keys tab of the XSplit Gamecaster window. Click on the grey bar next to the Overlay row and set a new hot key by using a single or combination of keys.