So, imagine you and your friends are playing a game where everyone gets to be in charge for one day. But then one of your friends decides they really like being in charge and won't let anyone else take turns. They start bossing everyone around and making all the rules without asking anyone else what they want.
Well, that's kind of what a military junta is like. A group of people in the military decide they want to be in charge of the whole country, even though they weren't elected by the people. They might take over the government by force, like a coup. Then they start making all the rules and telling people what to do, without really listening to what anyone else wants or needs.
This can be really bad for the people who live in the country, because the military leaders might not care about things like human rights or democracy. They might be more interested in keeping power for themselves and making sure everyone follows their orders. So living under a military junta isn't always a good thing.