The Progress page shows your grade on various assignments, which may be grouped by assignment type. The average is the percentage of points you have earned so far for a particular assignment type out of the total possible points for all assignments of that type.
As you complete more of the course and earn more points on that assignment type, the average will increase.
For example, if there are 4 assignments labelled 'Check for Understanding' in the course, and you've only completed one of them, that's 1/4 of the 'Check for Understanding' assignments. After you've completed all 4 of them, your score for that assignment type will be as high as it can be.
For details on individual problem scores within an assignment, see View Your Grading Details.