Your imagination is almost always worse than reality. Similar to you, I bet there are lots of other people feeling awkward or unsure of how to navigate social situations. It's totally OK to cue people in to your situation. You might say "I don't know many people around here" or "I'm new around here and trying to figure things out".
I highly suggest going to on-campus activities or joining a club (on or off campus) that has regular meetings. Also, consider doing some volunteer work. Volunteering is great because there are often many opportunities where you NEED to talk to people to learn what to do or to get the work done. A nice perk of volunteering is that by doing something helpful for others, it often makes an individual feel better about themselves :-)
During grad school, I didn't have a lot of good friends on campus, but found that my off-campus activities were much more rewarding. The university is a sort of default, built-in community, but it doesn't have to be your ONLY community. Find what feels good to you, and then keep doing that.