Summarize the following:
It's a purple star-shaped app with a white movie camera icon. It's at the top of the window.    You can save it directly to a project or add it to your iMovie Media Library to use later. Use the menu on the left side of the window to select the folder or location where your video(s) are saved. Click a camera in the "CAMERAS" section to record a new video. They'll be listed on the right side of the window after you've selected the folder or location where the videos are saved.  Hold the ⌘ key while you click to select multiple videos. Alternatively, click Import All in the lower-right to import all the media from the folder or location you selected. The selected video(s) will be imported to the destination you selected in iMovie. To add the video to another project, double-click a project under the Projects tab, then click My Media in the upper-left, and drag the new video down to your project's timeline.

Summary:
Open iMovie. Click the Media tab. Click File in the menu bar at the top of the screen. Click Import Media…. Click the Import to: drop-down at the top of the window. Click a destination for the new video. Select the location of the video. Click the video(s) you want to add. Click Import Selected in the lower-right.