What version of Premiere Elements and on what computer operating system?
If you are referring to the Split Screen effect, the generalized description for now
1. Clip on Video 1
2. Clip on Video 2 directly above video on Video 1.
3. To each apply a 50% crop...see Transform/Crop in project's effects.
4. If you want the clips to face one another, apply the effect Transform/Horizontal Flip to the right one.
More details when you describe more of your situation.