There's no option specifically called "Split Frame." All
you have to do is toy with the Cut/Crop feature.
Take your two video clips (person one and person two) and
lay them on top of each other in two separate video tracks.
Then for each of them, go to the Cut/Crop feature and
resize the boxes until one clip is shown next to the other.
Perhaps someone else can explain how to exactly do it
better than me, this is just an overview.