All activities with grading are gathered automatically in Grading report. Click Grades on the left side bar. In a grading table, you see list of all students and all activites (grading items) in your workspace. The last column, Course total, calculates and shows automatically the course grade, based on your settings.
As a default, the aggregation method is Simple weighted means of grades, and the maximum grade is 100.
You can change the aggregation method: Grades -> Gradebook setup -> click Edit on the first row -> Edit settings -> Choose one in the Aggregation menu (eg. weighted means of grades or natural, meaning sum of grades).