In the United States, when kids go to school, they have to do work and take tests. After they finish their work, their teacher gives them a grade to let them know how well they did. Grades are usually given with letters like A, B, C, D or F.
"A" means that the kid did a really great job and knows the material well. "B" means they did well, but there were a few mistakes. "C" means they did alright, but they could have done better. "D" means they didn't do a very good job and need to improve. And "F" means that they failed the assignment or test and didn't understand the material at all.
Sometimes, teachers also use pluses or minuses to make the grades more specific. For example, if a kid gets a B+, it means they did better than someone who got a B, but not as good as someone who got an A-.
Grades are super important in school because they help the kid understand how well they're doing and where they need to improve. It also helps their parents and teachers know how they're doing so they can help them learn better. Getting good grades is also really important for the kid's future because it can help them get into a good college and get a good job.