People might already know how it works in America, but I can show all of the ways it can be written:
the scale is from 100% to 0%, though they just have the number and not the "%".
0-52 (F-) - failing grade. if it is a test, you must re-take.
53-55 (F) - failing grade. if it is a test, you must re-take.
56-59 (F+) - failing grade. if it is a test, you must re-take.
60-62 (D-) almost failing, very bad grade. Sometimes it is failing, but it depends on the school. Usually you must re-take if it is a test.
63-65 (D) very bad grade. Sometimes it is failing, but it depends on the school. Usually you must re-take if it is a test.
66-69 (D+) bad grade. Sometimes it is failing, but it depends on the school. Usually you must re-take if it is a test.
70-72 (C-) not-good grade. It is a passing grade, but can be better.
73-75 (C) fair grade, but can be better.
76-79 (C+) not a bad grade, but not very good either. It is the minimum of what people might call a "good" grade. (because they only want to pass high school)
80-82 (B-) good grade. It shows potential, and you might have just missed one or two problems by accident. (because some tests have VERY few problems, just so they can be easy)
83-85 (B) very good grade. If you maintain an average of this or higher, you will be noticed.

86-89 (B+) excellent grade. People will think you're pretty smart!
90-92 (A-) Great grade! This is very good, because people think of students by a letter they usually get. So, if you have an average of this or higher, you will be called an "A student," which is an honor.
93-95 (A) Awesome grade! You're a genius.
96-100 (A+) PERFECT!!! Usually, the VERY best grade you can get.

101+ (A++) BEYOND PERFECT!!! You can only get this grade if you get ALL answers right, and then get extra credit right.
There are also a few other systems, like GPA, (which 4.0 is highest, and 0.0 is lowest) but it's NOT given as an assignment grade. It is usually just for overall grades. Standardized tests also have different, very weird grades. The PSAT goes from 0-240, and the SAT goes from 0-2400. On those tests, a 150 for PSAT and 1500 for SAT is a good grade.