A: If you want to insert B-roll in the middle of a video, split the video and drag the B-roll between the clips. To overlay it on the same screen, use the picture-in-picture (PiP) feature. You can find more details in these guides:

How to Add Video Clips and Images from Stock Media: https://help.flexclip.com/en/articles/7237820-how-to-add-video-clips-and-images-from-stock-media

How to Add a Video Layer (PiP): https://help.flexclip.com/en/articles/7237817-how-to-add-a-video-layer-pip