You can absolutely talk to absolute strangers.

There are two ways on how to not be a creep:

1. You start in a form of comments: Something happens, you comment it. More to yourself that to them. And if they respond you can continue.
2. You randomly catch them looking at you. It must be random. You should not stare under any circumstance. Then you smile. If they do not smile back. Stop. If they do, you can repeat that a few times. And if successful then you can approach them with a simple general question like “are you returning from work?”. (Note “Where are you heading?” Can be considered creepy and stalker like).

At any point you must be attentive and if they are uncomfortable immediately stop engaging.

But this is a bad way to make a friend. Those are people you should expect to never see them again. This is just a way to make someone’s day better. This is never meany to be anything more than a casual conversation with a stranger.