I had a brief interaction today that just left me feeling like I should've done something... but unsure what.

I work night shifts, so I just had to take care of some errands today. Last thing on the list was just picking up some groceries. As I'm checking out, just kind of a silly thing, the cashier starting ringing up my items for the girl in front of me; not really anything. We catch it, the girl in front of me is still bagging her stuff (she had a lot more than I did), but we just joked a little bit as we bagged out stuff. We ended up just chit-chatting as we walked out, and she seemed really friendly.

It was a pleasant interaction, but I sort of felt like "maybe I should... ask her out or something?". But I just couldn't muster up any sort of confidence, or even an idea how you just ask somebody out. Hell, do you ask someone "to grab coffee sometime"? Do you ask for a number? Hell, do you even ask someone you just met casually?

I really have no idea what the hell I'm doing.