How to split the screen in a music video.

Alright, any help will be sweat off my brow for sure. I have a music video in which I play the guitar and sing for most of the video. But I also play a harmonica lead in the middle of the song. I want to split the screen at that point so that one of me is on the left playing guitar, the otheer on the right playing harp. Then when the lead is over, it should go back to only the guitar playing video. What I need is step by step instrucitons on how to do this... the youtube videos are made to confuse I do believe. Keep in mind I am a novice so I need it step by step. Again, any help--much appreciated!!!