Share 'Proper clamping technique'

Hello, How do you properly clamp boards for screwing when screws are going inside the cabinet? How- To videos show how to do this if screws are to be on the outside. When I try to attempt this by using the right angle clamp, it throws my work out of flush when I try to clamp it. Without a drawing it might be hard for anybody to understand what I mean. What am I missing here? Thanks everyone.