You can capture your entire screen or just part of it and it includes voice recording. It is available for Windows, Mac and Linux. Just go to the site and click "record now" or sign in.
The Basic (free version) includes YouTube integration, instant download, short links, and the ability to play on any device. There is a 150 min video limit and videos expire after 2 months. If you find that you really need more features, you can upgrade to premium for $10/month or $60/year.
This is a great resource for recording your screen for web casts, lectures, professional development and more.