1) On your Mac, open Photobooth (icon pictured here) by finding it in your dock or in Applications. This program can capture still images or video.
2) If you want, add effects (sample shown here) to still images. This feature works best when you are in front of a solid, simple background.
3) Make a video by clicking on the button marked with a flim strip on the left below the screen, and wait for the countdown.
4) To upload the video within a post or page you need to use the add media button above the text editor (it has an image like camera with a music note and says “add media”). Once your file is uploaded, click on it and copy the File URL which appears in a text box (should have */file/* somewhere in the url, and should end in .mov). Don’t actually insert the files, but grab the URLs (ie: copy them using command+C). And make sure you’re not grabbing the link to the attachment page, but to the file itself.
6) Then write the post and embed the video by clicking the Q button on the toolbar (for Quicktime). It will ask you for that URL you grabbed (ITFs and admins, make sure the Viper Video Quicktags plugin is activated and Quicktime is enabled as a button in the Viper Video Quicktags Settings).
This will work with iMovie, or any other movie filmed with a Mac program as well! (All mac-produced videos will be classified as mp4.)