Okay kiddo, have you ever played a game where you had to call your friend over to play with you? Well, that's kind of like what a summons is.
In the grown-up world, a summons is an official paper that tells someone they have to go to court. When someone wants to sue someone else or make them go to court, they usually have to send them a summons.
Think of a summons as a message from the court that says, "Hey, we need you to come talk to us about something." The person who gets the summons has to show up in court, or else they might get in trouble.
So, just like how you call your friend to come play with you, the court is "calling" someone to come talk to them about a problem. And that's what a summons is!