|Select the screen or part of it as video source|
First you need to have a capture profile with the 'Desktop' as video source selected and active. Learn about 'Capture Profiles'.
If you're using the Desktop as video source all you have to do click the 'Window/Region/Frame-Rate' button on the Main Toolbar, or double click the mouse left button inside the capture window, or open the 'Profile Settings' dialog, and click the 'Video Settings' button.
To select a window check the 'Window' checkbox and then drag the finder icon and release it over the targeted window such as the Windows Media Player video window for example.
To select a region check the 'Region' checkbox and then click on 'Select' and use the mouse left button to start and end selecting the targeted region.
To select the entire screen simple check the 'Full-Screen' checkbox.
The Capture Frame Rate defines how many frames per second will be captured and you might want to change this to record videos like YouTube or Google Video for example. Note that the higher the frame rate you select the more CPU will be consumed while recording.
Also, for on-line videos or media player videos you should set the frame rate to 20-24. Learn more about the correct frame-rate to set for video capture.