When adding your inputs in Livestream Studio, one source you will notice is your computer's screen. Select this to add a local screen capture as an input.
This feature is ideal for systems with multiple monitors connected (e.g. Livestream Studio on one monitor, and a slideshow on another monitor). Please note that local screen capturing will increase CPU.
Save your settings to see the screen in your multi-view. You can transition it into Program the same as with any other input.