What is the best way to approach and ask out some girls in my class and in social events?

I talked to a girl at an event and hit it off with her. I paid attention to what she said and wished the girl a happy birthday. I almost never see her in person BUT I have her Instagram.

I met another girl in my class, and we hit it off by talking about our hometowns, majors (we are both computer science), and she always smiles and makes eye contact with me if we see each other. She is currently sick with a cold, and I have wished her to get well soon. She commented on my IG posts and even voted for an option in an Instagram story I made, regarding the Super Bowl.

There are also some girls in my Yoga class. How would I approach them after the class?

How should I ask them out?