Grade Scale: The scale displayed is the scale that has been applied to this specific grade book.  If the displayed scale is incorrect, contact your administrator to have it fixed.
Weighting Scheme: The weighting schemes are the 4 different ways your grade book can be calculated.  To select or change a weighting scheme, click the button of the weighting scheme you would like and the system will refresh automatically with the change.
User Defined Category Weights: Every grade book has categories for the events you create which will help you to organize your grade book, as well as help the system determine how to average final grades.  If you have chosen 'Category Weighting' as your weighting scheme, then you will want to make sure and set the weights for each category.