To get out of the 'double screen view' (studio mode), click the 'Studio Mode' button in the bottom-right next to the 'start recording' button.
Here's the quick-start guide:
OBS Studio - Free and open source software for live streaming and screen recording - obsproject/obs-studio
obsproject.com
I'd also recommend watching the Nerd or Die tutorial video series:
Welcome to our OBS Studio tutorial series! In this series we're going to cover everything that you'll need to know to make your stream look great.Next Video...
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