Turn on your Internet browser. Go to YouTube, or any other video sharing site.
Type in "Mashup" into the the "Search" field, and press "Search." There are many types of mashup videos. Some interesting links are listed in the "Resources" section of this article.
Look through these examples to get an idea of a mashup structure. Do this in order to prepare yourself mentally or to seek inspiration.
Open up your Internet browser. Play some movie clips you like, with the intention of telling a different story than was originally intended. Look at "Resource 3" for inspiration.
Open up RealPlayer Downloader before playing the clip. Play the clip, and press "Download" within the "RealPlayer Downloader" window. Press "Convert" next to the "Download" button. Click on the "Convert To" button within the RealPlayer Converter. Select the "PC or Mac" setting then press "OK."
Open iMovie. Go to "File" > "Import" > "Movies." Look for the film clips and press "OK". Watch the part of the clip that you want in your mashup, then click and drag across it to make a yellow selection box appear. Use this to select the part of the clip that you want and then drag it to the timeline.
Remember to have an idea of what story or feeling you want to convey while you edit. Make the horror movie into a romance. Make the romance into a horror flick. Go to "Share"> "Export Movie." Click on "Large," and press "Export."
Open up GarageBand. Drag the video you just made into GarageBand. Click on the "Eye" icon at the bottom right. Click on any one of the tracks with blue avatars since these are whole songs. Add a song appropriate to your mashup.