"Leave to enter" means permission to come into a country like when someone is traveling from one country to another. It's like when you knock on someone's door and they ask why you want to come inside. Before you can go into their house, they have to give you permission.
When someone travels to another country, they usually have to ask for permission to come in. The border officials might ask them why they want to enter the country and how long they plan to stay. If they get permission to enter, they have "leave to enter."
It's important to remember that not everyone gets permission to enter a country. Just like some people might not want you to come into their house, some countries have rules about who they let in. They might not let someone in if they have a criminal record or if they don't have enough money to support themselves during their trip.
So, in simple terms, "leave to enter" is like getting permission to go into someone's house when you knock on their door, but instead, it's when someone is trying to come into a new country.