There are 3 useful effects, Green Screen, Cinema21:9, and Mosaic.
First import the media files with a green screen. Find the GreenScreen in Montage effects, then drag it to the timeline on your media files. In the Properties Window on the right, click the Enabled button, select color be green. Then the green screen on your video or picture will be removed and only characters will be highlighted.
Also, you can choose other colors you want to remove.
About remove the green screen, just uncheck the Enabled option.
Drag the Cinema21:9 to the timeline. Drag with the mouse to adjust to the position you want to add. Also, you can change the duration.
Drag it to the timeline. You can change the size In the preview window. Click it, and hover your mouse to the border, find the green circle, drag it to change the size.
Or you can change the scale, rotation, and position in the Properties Window.
Also, you can change the Intensity of Mosaic.