I recently did a quick overview of how to install OBS here. The process to add display capture is as follows: –
- Click the “+” button in the “Sources” area

2. Select “Display Capture” in the list that pops up

3. Under “Create new” accept the default or name your display as you’d like and then click “OK”

4. Select the display you’d like to use and click “OK”

…and that’s it. If you’d like to add a webcam then take a look here.
Hope it helps!