Mac wont shut down due to an interruption of settings

Hello,

I just purchased my Mac yesterday and I was trying to get my photos to sync on iCloud. I would put in the password to allow the change but then I would be unable to turn it on without it reversing back to being off Doing this it then got stuck on the page where ti asks for the password and it turned almost a grey like tint. I have tried quitting out of it but it will not allow me to and I have tried shutting it down completely but it will also not allow that due to it being open. I was wondering how I can fix this issue.