Let's pretend you have a toy that your friend broke. You tell your mom what happened by saying, "My toy was broken by my friend." This is using the passive voice.
Passive voice is when you talk about something that happened, but you don't say who did it. Instead, you focus on what happened to the thing that was affected.
For example, instead of saying, "I made a cake," you could say, "A cake was made." In this sentence, you don't say who made the cake, you just say that it was made. It's like you're removing the person who did the action from the sentence.
Sometimes we use the passive voice because we don't know who did the action, or we don't want to sound like we're blaming someone. But usually, it's better to use the active voice, which is when you say who did the action. Saying, "I made a cake," sounds more clear and confident.
So, remember: passive voice is when you don't say who did something, and active voice is when you do say who did it.