Download OBS Studio from this link;
https://obsproject.com/download
Click PLUS sign under “Sources” tab;
Select “Display Capture” from the list;
Click “OK” in the next “Create/select source” dialog making sure “Create new” radio button is selected;
Click “OK” in the next confirmation box;
Click “Start Recording” button and then you can switch to your desired app or YouTube video/audio which you wish to showcase in your recorded video file and continue talking while you record since your talks or voice will also be recorded as per the option “Mic/Aux” which is enabled as below.
However, if you wish to not record your own voice and keep your MIC muted and record only the desktop audio from your Windows desktop, then click on the audio icon under “Mic/Aux” to disable the built-in microphone in your computer or slide the volume button all the way back to the zero bauds as below;
When you are done recording, click “Stop Recording” option under the “Controls” tab;
To view your recorded file, click “File” menu and click “Show Recordings”;
Your recordings in MKV video file format are usually stored in the “Videos” folder as below;
Notes 