In a large group of people like a classroom or a conference, people are trained to raise their hands when they want to speak. The leader of the group then "calls on" one person to speak. When you call on a person, it's common to say "Yes" and then either:

• the person's name
• an explanation of where the person is
• a description of what the person looks like

For example, these are all ways to call on someone to speak in a big group of people:

Yes, Karen.

Yes, you up here in the front.

Yes, the gentleman in the green jacket.

Yes, Dr. Phillips.