Watching lightning from inside your house or outside on your porch or inside a building is safe and it won't damage your eyes.
I love to sit out on my porch during a thunderstorm and watch the lightning and have my coffee.
Just don't stand outside where the lightning could strike you because if the lightning is close enough and strikes you it could injure you or kill you.
So be under cover somewhere and watch the lightning from a safe place.
If someone does get struck by lightning you can safely render first aid to them and call 911 for help.
You're safest in your house or a sturdy building when it's lightning so avoid standing outside in the lightning storm.
Thunder will not hurt you but the lightning that follows will hurt you if it strikes you but it's okay to watch the lightning from a safe place.