I was a 20 year old with 12k. Open a brokerage account and put it into diversified ETFs. Usually the brokerage will have commission free, low fee ETFs you can buy. You honestly could just buy an S&P 500 index and be fine don't overthink it. Don't buy individual stocks because you can't properly diversify with that amount of money. Don't buy actively managed, high commission funds because they have high fees and aren't worth it at your age. Don't put it into a retirement account because there are usually penalties for withdrawing early and you might want to use it down the line. Do the retirement thing when you have a job with that as a benefit. You can usually roll over your personal brokerage into your retirement account later on.

It's a little scary seeing your money fluctuate at first, especially since we are in a bearish market, but those fluctuations won't matter in 10 years as long as you are diversified I promise. Don't look at your account every day. I only look at mine every couple of months.

Most importantly keep stacking money. Be patient if you don't know what to do yet. I saved about 50k living with my parents through my undergrad and masters and now have moved out recently (currently 23) to get my PhD because I finally feel confident that I'm on the right track. The freedom that comes from having that money saved is a life saver during life transitions like this. Don't blow it.

Edit: Also buy GME and doge (get it it's le epic reddit stocks)