There are many screen capture applications out there which you can download to use. Presenting ScreenJelly, an online service that lets you record whats going on your screen with your voice. The interface is real simple,  just hit the record button and it will start recording. Afterwards you can also share your video through email or twitter.

It also gives you the ability to make anything you record “private” else it will go on their website in public recordings section. You can sign up for free and takes less than a minute.