When you create empty roles in the schedule, roles that don't have spots filled, they show up as opportunities to volunteer on the volunteer dashboard.
So go to the schedule, create a role for a specific week, such as scripture reader. Leave the name field blank.
Save it.
On the people menu, choose volunteer... it should show the scripture reader as a checkable box.
Check it.
Go back the schedule-- your name should be in the dropdown box but not 'saved' - red text will appear next to your line saying "Volunteered." If you accept the volunteer, click the save icon.