G.P.A. stands for 'grade point average'. Your teacher or professor assigns a grade letter to you based on your performance in the class, homework and exams. An 'A' =5, 'B' = 4, 'C' = 3, 'D' = 2 and 'F' = 1. The average is all of your grades (in number format) divided by the number of classes you have taken. For example, if you had an A, B and D that would be a 5+4+2 = 11, which you divide by 3 classes to get a GPA of 3.66.
A GPA of 3.0 means that this average meets or exceeds '3.0', which may be used to qualify you for enrollment into classes, colleges or scholarships.