Workflow Rule for populating a field with another field

I need to populate the contact address with the primary account address if the contact address doesn't get populated upon save.

This has not worked. It's an example of populating just the city portion of the address: FieldValue[<Primary City>]=FieldValue('<AlternateCity>')

I was not using a workflow, but filling in the default value on the contact address field.

Any suggestions as to where I can get good help for creating workflows?