I do not understand:
The thing you want is buried deep in categories. I don’t know of a way to set percentage directly but you can put points on the category itself and Moodle will calculate percentages from that. Once you’ve set the category, then click on the settings for that category and set the points. Make sure you also include empty items (items students gave not turned in at all) or your percentages will be off. You have to click on “see more” to make that option visible.