As with file sharing, you'll need to visit the Network and Sharing Center in the Windows Control Panel, click Change advanced sharing settings, and enable "file and print sharing." Macs and Linux PCs can't connect to homegroups and use the more convenient sharing features built into modern versions of Windows, so you'll have to set up printer sharing the old fashioned way.
Visit the Printers list in the Control Panel, right-click the printer you want to share, and select Printer properties.
Click the Sharing tab, enable sharing for the printer, and give it a name. You can also enable printer sharing while setting up a new printer.