In this tutorial you are going to see how to use chroma key in shotcut

First import normal and green screen videos. Add a video track, drag and drop the video on track. Click on the play button to check the video. 

Add another video track, drag and drop the green screen video on this track. Click on the play button to check the video. Click on green screen video track, click on filters.

 Click on add a filter and search chroma key:simple, click on it to apply. Because green color is already selected color in key color option it will get removed or you will need to select the green color from screen by using pick color from screen tool (eye dropper icon) You can change the distance slider settings as per your need to make visible or invisible the green color. Click on the play button to check it. 

 Change position & size- 

To change the position of green screen object add size and position filter. Drag the corners of it to change the size and drag and drop it where you want it.  

In this tutorial we will see how to use green screen in shotcut video editor.