Open the video-editing program you will use to overlay the videos. You may use native programs in your operating system such as Windows Movie Maker for Windows or iMovie for Mac, or another popular program like Adobe Premiere, Final Cut Pro, Avid Media Composer or Sony Vegas. While each program requires more specific steps for the editing process, the concept of editing on a "timeline" and placing video footage on specific video tracks remains the same regardless of the editing program you use.
Import the videos you want to overlay. The "Import" function is typically found under the "File" menu. Some programs allow you to use the drag-and-drop function to readily import the footage into your project's Import or Project window.
Drag the first video into the first video track found in your Editing Timeline. This timeline is where the actual editing process happens. Using the editing tools available in your program, you can cut, splice, alter the playback speed or change the size, color and other attributes of your selected video clip.
Press the "Play" button to look for the thin, vertical line that allows you to view the video from the Editing Timeline (most programs allow you to use the computer's space bar to start or stop the playback). You will be able to view the footage on the Preview Monitor. The playback starts where the vertical line is set. If you want to start playing the video from the very beginning, simply drag the vertical line on the leftmost part of the video.
Drag your second video into the second video track, which is located on top of the first video track. Most video-editing programs can accommodate dozens or even hundreds of video tracks, although only a handful are used in most productions. Any video you place on top of another video becomes the default video shown on the Preview Monitor. This means that the video on the second video track will be the only one viewable. If you place a third video on the third video track, this will become the default video viewable on the Preview Monitor.
Click the video clips you want to combine together in your Editing Timeline to highlight them. Use the "Overlay," "Composite" or "Superimpose" function in your editing program. The overlaying will be done on the entire duration of the video clips highlighted. If you intend to overlay only a specific part of each video, you have to separate the exact part of each clip where you want to apply the overlay function by using the "Cut," "Razor Blade" or any similar function that refers to the cutting of a video clip into your preferred selection.
Render your overlayed videos. This is the process of generating a new footage based on the effects or any other function you use in the video clips found in your Editing Timeline. The "Render" function is usually an option you have under the "Sequence," "Effects" or "Video" menu. Most programs use the shortcut "Ctrl-R" or "Apple-R" to start rendering selected video clips on the Editing Timeline.
Export your final video according to your preferred video file format. Popular formats that are typically used to burn DVD movies, watch the video in a media-playing program or transfer the video to a multimedia device include MP4, MOV, AVI and WMV.