Enter each course with its grade and credit hours to get a properly weighted GPA. Weighting matters: a four-credit course moves your average four times as much as a one-credit one, which is why the unweighted mean of your grades is usually the wrong number.
Multiply each course grade point by its credit hours, add those products, and divide by the total credits. An A in a 4-credit course contributes 16 points; a C in a 1-credit course contributes 2. Together that is 18 points over 5 credits, a GPA of 3.6.
Two different meanings are in circulation. Credit-weighting, which this does, accounts for course size. The other sense adds a bonus for honours or AP courses and can exceed 4.0. This calculator uses the standard 4.0 scale without course-difficulty bonuses.
Yes. A- is 3.7 at most US universities but some use 3.67, others do not use plus and minus at all, and many countries use entirely different scales. Check your institution before relying on any figure for an application.