How to carry on the conversation in day game?

So yes it takes a lot of guts to approach pretty women. Some of the days I can't seem to approach because it takes a lot of courage.

I'm an Indian guy, I remember once these 3 very pretty english females who looked around 18-19 as I walked past them waiting for the train said "sex" and unfortunately I was too shy to approach them. They was even looking at me. I was wearing shorts that day.

What do I do in the situation:

Me: I just saw you and just had to say hello to you!

Her: Hello with a smile

Me: So what are you up to?

Her: Just going home (with a smile)

Me: Ok good luck

What can I say in this situation?