This final step - Act - is about actualizing what we had decided in the earlier step of Look In. 
Act involves either: act of commission - to commit to doing something, whether continuing with what has been done before or undertake a new action which we believe is right to do, OR act of ommission - to stop doing something we now believe is not right to do. 
The quality of Act (actualization of intention) is a consequence of the commitment one reaches during the Look In step.