As another commenter said, situational commentary is a good way to start a convo with a stranger.

But your deeper issue is almost certainly anxiety. The real way you learn to start conversation is by just saying whatever the fuck. Then notice if people are interested, amused, confused, angry, etc - and then continuing from there. Over time, you naturally, without trying, start thinking of things which garber positive reactions from others, and become more adept at guaging their reactions, which drives further inprovement. Anxiety hinders you on both of these fronts - taking action (saying something) and noticing peoples reactions.

Be aware of this anxiety, notice it, and remind yourself that it doesn’t actually mean anything. If you say something weird, so what? Lots of people say weird things in college. That’s what college is for. Being a good conversationalist is a skill, and as a skill, you will suck at it at first. Sucking at it is simply part of the process. So allow yourself the ability to suck at conversations long enough to get good at them.

If you know you are going to be in an informal group setting (for example, going on a camping trip where everyone will be sitting around a campfire), get a copy of the book 3000 Questions About Me. Everyone takes turns thinking of a random number between 1 and 3000, and then everyone answers the question. It’s kind of a fun game, but it gets deep really fast.