A "grading" is where your knowledge and proficiency in karate are assessed. This takes place in the club with the senior dan grade instructors.
Students are invited to grade when they are ready, so you will not be asked to do anything that you should not be able to do well.
The grading syllabus is available from the chief instructor.
If you successfully pass the grading you will receive a certificate and a belt of the colour that represents your achieved level.
It should be noted that in your karate career, gradings are relatively unimportant and are a by-product of good training. The aim of karate practice is not to get to the next belt. Neither is it the achievement of obtaining a 1st dan (black belt).
To focus on grading and the colour of your belt is wrong.
A student who has obtained their first black belt has not arrived at their destination, they have only just started the journey.