During the short time when the moon completely obscures the sun – known as the period of totality – it is safe to look directly at the star, but it's crucial that you know when to take off and put back on your glasses.
First and foremost: Check for local information on timing of when the total eclipse will begin and end. NASA's page of eclipse times is a good place to start.
Second: The sun also provides important clues for when totality is about to start and end.
Learn more at https://eclipse2017.nasa.gov
Find more videos about the solar ecilpse on the Sun Eclipse 2017 gallery page.