First, you are looking at the footage window, not a comp window. Second, We don't know anything about your composition settings. It looks like you need to start here first: Basic Workflow.
When you have spent a few minutes watching these 3 tutorials then come back to your project. Import a video, check the properties, then select the video in the Project Panel and go to File>Create Comp from Selection and start working in the composition timeline and timeline.
This is a bit off topic, but After Effects is a poor tool for editing video. It was never designed to be one. Technically, you can edit a video in AE, but the process compared to a dedicated editing package is cumbersome and not worth your time. If you have the full CC subscription, you should use Premiere instead.
also,unless you are deliberately doing so for some reason, shoot your iPhone videos sideways not vertical.