An optional step is a step that is not necessarily required to successfully complete a run session.
During a run session, if the object of an optional step does not exist in the application QTP bypasses this step and continues to run the test
To set a step as optional in keyword view right click on the step and select Optional Step
Alternatively, you can directly write the keyword "OptionalStep" preceding a statement to make it optional
Following video describes an OPTIONAL STEP and how it can be used.