A little awkward, but not too bad, even for an extremely introverted person like myself. Chances are the people who are there already were at one point in your shoes when they first attended. If you're nervous you can always post to/comment on some of the group's stuff, so that when you arrive you can be like "hi, I am username so-and-so" and they will be like, "oh, yeah! I saw your comment..." and so on. Not all groups are great, but my experience has overall been quite positive.

Also, it's pretty commonly understood that the site exists so that like minded people can find each other when they otherwise likely wouldn't have crossed paths, so it's a great way to make new friends (and/or social networks). If you still have some anxiety, I would suggest contacting the group admin and saying you're interested but a bit nervous about going to the first meeting. It does take a small amount of money each year to host the group, so the people in charge of it usually care enough to try to make people feel comfortable enough to come and keep coming. (I have a friend who runs a small meetup group for writers, and he's always extremely super thrilled when new people come out to it.)