Okay kiddo, so imagine you live in a house that is surrounded by other houses and there is no road that goes directly outside of your neighborhood. That means, you have to cross other people's backyards or go through their houses to get to the main road.
Now, just like this, a landlocked country is a country that is completely surrounded by other countries and doesn't have any direct access to an ocean or a sea. It's like living in a neighborhood that is completely surrounded by other houses and there is no road that leads to the outside world.
Because of this, landlocked countries have to rely on their neighboring countries to transport things like goods and people through their land or waterways. This can often make things more difficult, expensive and time-consuming compared to countries that have direct access to the seas.
So, that's what a landlocked country means in a nutshell, it's like living in a house surrounded by other houses with no road that leads outside.