Click this link: https://obsproject.com/download to download the software.
Select your operating system
Click on Download
Click “Run”. Go through prompts accepting defaults.
Once OBS has launched you will want to create a screen and enter capture devices (microphones, cameras, monitors, capture cards, XLR interfaces, etc)
If you have your stream URL and key configured you will want to click on “Start Streaming”. If you’re using Facebook Live you can check out this tutorial here http://techmikewi.com/2020/04/14/how-to-get-your-facebook-live-stream-key-for-obs/
If you want to record to your PC for future editing click on “Start Recording”