Open the application Photo Booth, and make sure the video mode is selected. Yes, that's you in the little window.
Think about what you want to say, sing, yell, and make sure you are centered in the preview window of Photo Booth. Then click on the red center button. You will get a 3-2-1 countdown, and then your machine will start recording. When you are finished, press the same button, which is now a square. You can see the timer on the left. Try to keep these videos short for emailing, a 5-6 second video is a bit under 1 MB.
If it takes a few tries to get the one you like, no worries. They all go into a bin below.
Choose the one you like, click on the email icon.
The movie will be automatically attached to an email as a Quicktime file and will be ready to sent.
Happy New Year!