D2L's gradebook is set up to do simple points by default. If you would like to create grade items that are set to be a certain % of the student's final grade (weighted system), click Settings in the upper-right area of the gradebook, click Calculation Options, then select "Weighted" and Save.

After setting up a weighted grade book, creating items, and even entering scores, you can go back into Manage Grades and adjust the weights of assignments at any time. It won't harm anything.