Canvas organizes all graded student work into Assignment Groups. Your course may already have some default groups like Assignments, Discussions, Quizzes; and you can create new groups to fit your grading style and requirements. Assignment Groups can then be weighted with a percentage to calculate the final grade.
Weighting is done in the Assignments page rather than in the Gradebook.
You can drop a specified number of lowest or highest scores from an Assignment group. Note: when dropping grades, a student must have at least one more submission than the number of grades being dropped. For example, if you are dropping the 1 lowest grade in a group, a student must have at least two graded submissions in that group before the grade will be dropped.