Start Buttons:
Start the Shadow timer!
You will be asked to confirm that it is OK to shadow to the default backup folder (read the help there).
Your shadow set will then be validated and on your acceptance, shadowing will start.
The very first run will take a few minutes (dependent on the amount of data you are shadowing). Subsequent runs will be much faster, probably just a few seconds. 
If you make a change to the shadow specification, the timer will stop and you must re-start it with this button.  
Once set up, Notebook Shadow runs automatically and requires no manual intervention.

Run button:
Press this to perform a full 'scheduled' run at any time.  This is useful if you have backups scheduled for lunch time only and want to run one at a different time.

Stop button:
Press this button to stop shadowing at any time.