You wish to create categories of volunteer skills and areas of interest. These can be used for volunteer registration.
To create categories of skills and areas of interest for volunteers, go to People -> Volunteers. Here you will see a button for Volunteer Skills and Volunteer Areas of Interest. Click on either of these to add or edit fields. You can add the different skills or times you require for the volunteer registration page.
After you've added these sections your volunteers will be able to select skills and areas of interest when registering.