You can follow these steps:
Click the Options button on the toolbar
Go to the Cameras tab
Select a camera from the list
Click the Properties button
Click the Motion Settings button
Select the Motion detection enabled checkbox
Use the slider to determine the Motion detection sensitivity
*When this option is selected video will only be recorded when motion is detected.
With regard to your other question, the program does not offer options to run always on top. NCH Software formally takes suggestions or feedback about our products through the form at http://www.nch.com.au/suggestions/