How can I approach & talk to a stranger or strangers properly?

I am currently in my 2nd year of college and objectively I am doing well but emotional intelligence wise I need to improve. All I know for approaching people is to approach them when the area is good or not as well as what they are doing that needs focus. There were two people that I find interest to talk to them but they were talking to each other & realize it would be awkward for me to talk to them since I didnt ask them if I would join in. Even if it was me & the person I dont know how to start a conversation with them nor figure out how to know them so that is where I am lost at.