Can someone explain to me how I purchase tickets on fandango if i’m going to a Regal cinema?

I would like to purchase tickets on Fandango to see Twilight on Friday @ 7:00 at a regal cinema.

I was wondering how that works? I know you purchase the tickets online but what do you do after that? What do you do when you get to the actual movies?

Please help and please check back after you answer because I might have more questions. Thank you!