There are two ways to assign services to a resource:
Assign a resource via the service settings:
Head to Setup > Manage Services
Find the service you wish to assign a resource to and click on the pencil icon on the right to edit.
In Availability > Resources > tick the resource(s) that will be providing that service:

Assign a service to a resource in the resource info settings:
Head to Setup > Manage Resources
Find the resource you want to edit and click view info > edit resource
You can then assign services to the resource by ticking the box(es):