Idle the chainsaw's engine as you approach the log to be cut.
Pull the trigger to increase the chainsaw's rpm and firmly place the bow bar's metal thumb against the log. The thumb provides a leverage point that provides stability for the duration of the cut.
Allow the saw blade to do the work of slicing through the log, maintaining a light forward pressure on the bar.
Release the trigger as the blade completes the cut, and withdraw the bow from the log to commence the next cut.