Older person calling a younger person

Hi I need help. I would like to ask, how does an older person call a younger person? For example, I want to call my younger sister. So I say (name)-ssi/(name)-ah? Can you explain what ssi/ah means~? Also, if I'm talking to person A/a group of people/an audience and I want to refer to person B(younger than me) how do I do it? Are there people who call each other using just names? For example chingus. They call each other by names right? What if someone asks about a friend, how does this person refer to his/her friend? I am really confused about this, and I'm sorry if I failed to make sense. Looking forward to a response! Thank you so much!! ^^