Attending a friend’s wedding alone. What do you do at the wedding as a guest?

I’m going to be attending a friend’s wedding in a couple of months. The only person I would know there would be my friend. Seeing that my friend would be busy getting married, I would likely be left on my own. I haven’t been to many weddings nor am I a very extroverted person. Any tips on the appropriate time to stay for the wedding and other general tips to avoid getting stuck in an awkward situation?