When and where to ask someone out?

Hi there. I am a bisexual cis male of 22, and as such, I feel attracted to a lot of people.

When I was at the supermarket for an extension chord with my brother, I found a guy about my age very very cute, he worked there. I found him so cute I told my brother I kind of wanted to have his number, and he encouraged me repeatedly to go ask. In the end he offered to go for his Instagram when I asked him half seriously too, and so he went. Turns out they knew each other beforehand but my brother didn't remember, and he gave me his Instagram, and we texted and now we are in a situationship.

The thing is, it did lift my confidence but at the same time didn't motivate me to really ask anyone out anymore. Not male nor female.

I am at school, and I don't want to hit on classmates because well, they're classmates. Would be very uncomfortable to share a classroom with someone who I tried to hit on and failed, or dated and also failed.

I am at the park, I see a gorgeous person reading something, sitting on a bench, having a walk, sometimes with a dog. I don't approach, "good morning" maybe, but that's it.

I'm get to a store and see the same pretty store clerk? Hello, just this thank you, I'll pay with card, goodbye.

Sometimes I even get acquainted with people from places I visit. A store nearby, I once had to return an umbrella and the girl at the desk gave me her number so I could follow up on the situation on WhatsApp. We did chat a little bit, and when I see her there I take some few minutes to chitchat. But I don't hit on her, because that would be a bit scummy? To like, have an acquaintance and then just get hit on.

I don't know, it just never feels right with anybody. I feel everybody will judge me or it is wrong and inappropriate in every setting and every situation to ask someone out. I don't do parties, but I once went to one and girls avoided me like the plague, so I guess that's not a place I really fit in.

So my question is where the hell and at what point is it appropriate to ask anyone out?