Okay kiddo, so you know how you have a bedroom in the house where all your toys and clothes are? Well, imagine that the police think you have something in that bedroom that you're not supposed to have -- like a toy that someone else forgot at school. If they want to search your bedroom to look for that toy, they usually need something called a "warrant" first.
A warrant is like a permission slip from a judge that says the police are allowed to come into your bedroom and look around. So normally, the police can't just barge into your bedroom and start looking through all your stuff without that permission slip.
However, there are some situations where the police don't actually need a warrant to search your bedroom. For example, if they think you might be in danger, or if they think someone else in the house is in danger, they can come in and search for things that could hurt you or other people, without waiting for that permission slip.
There are also some other exceptions to the warrant rule. For instance, if the police are chasing someone and they run into your bedroom, the police can follow them in without a warrant. Or if they pull someone over in a car, and they see something suspicious through the window, they might be able to search that person's car without getting a warrant first.
So basically, most of the time, the police need a special permission slip called a warrant to search your bedroom or any other part of your home. But sometimes, if there's an emergency or some other special circumstance, they can do it without getting that permission slip first.