Going to my first wedding as a groomsman, what do I need to know or expect?

Don't worry, all you will have to do is wear the suit and just stand there next to the best man and watch......if they have you walk down the aisle with a bride maid that all you do....if you and the other grooms are pitching in for the bachelor party then that all you need to do, you DON'T have to buy a gift....so enjoy..=)