You can view and pick up available open shifts from Schedule tab. Click Open shifts link on a calendar cell to view available open shifts for that particular date. The link will not appear if there is no open shift for the date. Click Open shifts available button at the top left to view available open shifts for all dates.
Click Pick Up Shift from the open shift list. If manager approval is enabled for your organization, then your request is sent to your manager and the shift will be assigned to you when your manager approve it. If manager approval is not enabled, then the shift will be assigned to you immediately.