Alright, let's imagine you have a group of friends and one day while you are all playing together, one of them starts behaving in a way that you find not very nice. They might be teasing you constantly or not sharing toys with you. In this situation, you might feel like you want to talk to your other friends and make a decision on whether this particular friend should still be part of the group or not.
Similarly, in a group of people like a country, there may be some individuals who behave in ways that are not nice - they may harm or try to harm others or they may be from a group that is considered to be harmful to others. The government that acts like an umbrella for everyone in that group, would consider whether these individuals should still be part of the group or not.
When a person is suspected of being part of a group or an organization that carries out dangerous activities such as terrorism or other things that can harm people or countries, they might be captured by a group in charge of security called the military, which is like a kind of police force that operates on a much wider scale. In this case, the military would determine if the individual is a threat to others, if they have any partners who are doing the same things, and if they are secretly working for some other group that is trying to harm their country.
The Combatant Status Review Tribunal (CSRT) is the process of the captured person being questioned to collect information on these issues. These questions are asked to ensure that the person being evaluated does not present a risk to others or their country, and they can help provide information for others who might be involved in dangerous activities.
To simplify, the CSRT is a process like checking if some people are nice friends who will not cause trouble, or if they are mean friends that could do harmful things, and if they should continue to be part of the group or not.