Students are constantly raising their hands for various issues. They may have a question. They may need to use the restroom. They may need to get something. The list goes on and on. Now, you can teach your students to let you know, generally, what their issue is going to be about. This way you can decide which issues to deal with first to stay on-task with the rest of the class.
If the students raise their hand and show you the number 1, that means they have a question about something that was just said or something they do not understand.
If the students raise their hand and show you the number 2, that means that they have to use the restroom.
If the students raise their hand and show you the number 3, that means they need a new writing utensil.
By using this simple system, you are able to address issues as they fit appropriately into your teaching.