‘Hold your horses’ is a popular idiom. It means wait and think before you go ahead and do something.
We say 'Hold your horses' when someone is rushing into something. We want them to wait a moment, to be careful and patient before acting.
Listen to these two conversations in which someone is told to hold their horses. What's going on? In the first conversation, Candy and her brother Jake are in a phone shop. In the second Max is talking to his girlfriend Jane about something that happened at work today.