If your college has a good org, even it it's a DSA chapter, join that. If your college doesn't have a leftist org, start one or (even better) join a local org in the community your college is located it. The best thing you can do is contribute to building mutual aid networks, or really any project that uplifts working people. And whatever you do, and I'm sorry if this comes of rude, do not do or say anything extremely online. Don't argue with people on Ukraine or Russia, the legacy of Stalin or the USSR, etc. Those are conversations best had 1-on-1 with people who you've already gauged as likely to be receptive. Also just have fun, university is a great time.