Ok. My instructions were a bit off. You tap to select then add to the timeline, not drag. Here is how iMovie looks and works. I've already created a new project using the Simple template; which adds the least effects.
Make sure you are in the Projects tab at the top, then tap the + icon at the top right to create a new Project; then choose your template. You can play templates to get an idea of the kind of movie they are meant to create.
{Thinking over what you say you are seeing, you might be in the Videos tab view, which just shows the more recent video clips in your Camera Roll. Go to Projects.}
These are the basic areas.
Video Preview shows the current frame, as determined by the white line in the Timeline.
Video Clips shows all videos stored in the Photos app. These are the clips a available for your project. You can also take clips in-app by using the camera icon at the lower right. Those clips will be added directly to the Timeline.
Timeline shows all clips added to the current project, in order of play, with any effects added before or in-between clips. This is also where you will do any editing of the clips.
With the above view, tap the clip you want to add to the Timeline, and then select the down icon.
{Tap the (?) icon at the top left, then More Help at the bottom left for online iMovie help. It will be pretty much the same thing as I linked before.}
Your screen should now look something like this. You are ready to export the clip at a new size, or do some trimming and editing before exporting.
Back out to the selected project view (or whatever it's called). Here you can use the export icon (looks like a box with an down arrow) to choose a destination for the movie, and then an export size.
Good luck.
