When you come up for a court martial it's never a good thing and means you done something serious enough to warrant possible prison time, jail time and even in some cases death.
A court martial is is empowered to determine the guilt of members of the armed forces subject to military law, and, if the defendant is found guilty, to decide upon punishment.
The punishment can vary depending on what the defendant actually did to get a court martial for and if you're found guilty you may either face jail time, prison time, fines and like I mentioned above you might even be sentenced to death and go on death row as a result.
Usually if you're found guilty and put on death row you will be executed within 10 years at most and there's no way of getting out of the punishment.
Some people who go up against a court martial may even face life in prison without parole.
You never ever want to go up against a court martial in the military because it means bad things.