Click the options button ("Options" on the Interface Diagram). Go to the Video Size setting and change it to a lower resolution. You want to keep it as high as possible without causing the software to "stutter" too strongly while you are recording. Save your settings.
Click the button that looks like a video camera. Your recording will begin. Click again to end the recording.
Your file will appear in the Preview Pane on the right. Double-click it to view it and make sure it is satisfactory. If so, drag the file from the Preview Pane to your desktop, shared drive, or USB flash drive.