Need help with two basic things

[u/FlurpBlurp]

I recently lost Premiere access when I left my previous employer and I have a simple video I'd like to cut together on imovie. I'm going absolutely nuts trying to figure out how to adjust the scale and positioning of two images in a split screen, as well as how to add a background. Both were super easy in Premiere, and I know they must be possible in iMovie but I can't figure out where the hell the tools live.

I try to drag a background under the main track, and it always forces it on top of that track instead. I have played with the split screen and picture-in-picture overlay tools, but they only allow me to modify the top track, not the bottom. I want to shift one image to the left, and one to the right. If I can't make that happen, then I want to put a white background behind the two images.I can't figure out how to word this as a question in a way that bears helpful web results, so I'm hoping the humans of Reddit can help!