On the top right side of the screen there is a gear for settings. Click it. It will take you to the "Manage Account" screen with 5 buttons to chose from, choose the one in the middle: "App Settings" Click it. You are then presented with a page that displays your Hub Works apps, Select "Zip Schedules." Click it. The next screen will display 3 buttons with the first one being "Positions." Click it. There you have it... You may now add more positions.
Took me 30 minutes to find it the first time and this time about the same. This should be an easy thing to find and I don't get why they keep moving it around in the background... Put it on the main schedule display page next to the "+Add Employee" button. There is plenty of room, and it should be quick to access, not hidden.