At this point, you're just about ready to start streaming. All that’s left is putting all the pieces in place within OBS.
When you open OBS, an empty scene should already be made. You’ll first want to add the game you’ll be streaming, so launch it now. Then, alt-tab back to OBS and right-click the empty Sources list. Select Add > Game Capture, then name the source and select the game you want to stream from the Application dropdown list and hit OK.
To add your webcam, make sure it’s plugged in, then right-click the Sources list again and select Add > Video Capture Device. Name the source and select your webcam from the Device dropdown list. If you want to adjust the resolution to something specific then you can do that here, otherwise hit OK as you’ll be able to resize the webcam in the scene viewer. Just hit Preview Stream then Edit Scene and you’ll be able to drag and drop your different sources around the scene with the mouse. When you click a source, it will get a red border around it and you can drag from the corners to resize any window.
Overlays should be added now too, but they're optional. An overlay is just an image or text superimposed over your stream, and can be as fancy as reskinning a game’s UI or as simple as putting your twitter handle on screen. To add an overlay, just right-click the Sources list and select Add > Image.
If the image is a PNG the transparent parts will remain so, which is how many streamers add frames to their webcams and other cool details. If you are streaming Hearthstone, consider taking a screenshot of your decklist, cropping it in Paint, and adding it to the side of your stream (see the image above for an example).
Be sure to consider what game information your webcam and overlays are covering up. Even blocking small UI elements can be frustrating to viewers. If you are planning on streaming multiple games, you can make different scenes that vary slightly in webcam size and placement to ensure everything is always in the right spot. Scenes are a great way to switch your stream up on the fly.