They will train you. Usually this means starting you on a quiet night a little before it opens. If you're still garbage at mixing the drinks they'll let you just be a barback until you get it down. It's not as hard as it looks and the only thing you have to get used to is the pour heads on top of the liquor bottles and the soda machines which can be finicky. Just go in with some basic knowledge of mixed drinks, like a margarita is tequila + lime juice + triple sec.
Being a bartender is a status boost and girls will want to talk to you more. Gives you a free and easy "in" to talk to anybody you want. Like if you were throwing a house party, you can chat to anyone you want because it's your house, right? As opposed to going to Chad's frat party where you don't know anybody. The difference is big.
I slayed quite a bit as a bartender but most of the success came from the connections I made through the staff, not actually working the bar. So after the bar closed up we would all go to another venue, like a VIP area of a club or a private club. Owner would parade me around in front of girls and be like "look at this new white boy on the staff he wants to talk to you" etc. So I guess my success here was more of a geomaxxing thing than a bartending thing. There were some exceptions, I think I went on 3 dates with girls whose numbers I got from talking to them at my bar.
Thinking about it more, there are many parallels between being a bartender and being a member of a fraternity in college. If you are interested in girls who work nightlife then saying "yeah I'm a bartender at X bar" is the best icebreaker in the world. Instant trust + attraction boost. Just like if you are in a fraternity at an American university and talk to a girl who is in a sorority, she might ignore you until she hears the magic frat word and all of a sudden you're one of the cool ones.
STEM guys are largely social retards but are also some of the coolest people I've ever met. I've discussed here before that the magic recipe is being a little bit non-NT but not so much that you're useless. A huge proportion of cool and successful geomaxxers I've met work in IT.