I'm sorry about the issue. Is there any error or message?
Was it working previously? Or is this a new printer or new computer, etc.?
What's the model of your printer?
Can you click on the Apple logo / menu, then click on About this Mac, then tell me your Mac OS X version, such as 10.6, 10.7, ..., 10.10, 10.11, etc.?
Is the printer connected to the computer with a USB cable? Or is the connection wireless?
Please reply at the box below. Thank you.