Installing Printer Drivers
Disconnect the printer from the iMac. You now need to install drivers for your printer so that Mac OS X can use it. There are two main ways to do this: download the latest drivers from the printer manufacturer's website, or use the CD/DVD that came with your printer. It is recommended that you download the latest drivers from the printer manufacturer's website because there is a good chance that the drivers on the CD/DVD that came with your printer are a bit outdated. Finding the manufacturer's website is very easy. Just do a basic Google search for the manufacturer of your printer, followed by the term "drivers". For example, if you have an HP printer, do a Google search for HP printer drivers. You should quickly find the manufacturer's website. Locate the drivers for your specific printer, download, and install. Upon doing so, you should enter the setup wizard for your particular printer. During this process, you will most likely need to connect your printer to the iMac. Upon completion of the setup wizard, you should have successfully connected the printer to your iMac, and you should now be able to print.
In a case where you would prefer to use the install disc that came with your printer, rather than downloading the drivers from the manufacturer's website, simply follow the same steps mentioned above. Upon inserting the disc into your iMac's CD/DVD drive, launch the installer and go through the setup wizard.
Please note; some install discs that come with printers are not Mac OS X compatible. However, this doesn't mean that your computer won't work with your iMac. Most likely, the drivers that you need can be found on the manufacturer's website.