How do I find info on creating and printing address labels?

That can depend on your iMac model and your OSX version, neither of which we know. In older Mac OS versions, you print mailing lables from Address Book; in newer OSX version it;s called "Contacts." Both come as part of teh mac OS--you need buy noting to get there.

In either, when you do the Print command, the option to print labels ins in the Print dialog box:

Note the selection by "Style" where I've drawn the red rectangle.

You can also set up and generate mailing lables by buying Microsoft Office:Mac