If your Mac keyboard has an Eject or F12 key in the upper-right corner, you hold it down for a moment to open the CD/DVD drawer , or, if you have a slot-loading CD drive, to spit out the disc that's in it. If it's an older Mac keyboard without an Eject key, you can eject a CD (or any other disk) by Control-clicking its desktop icon and choosing Eject from the contextual menu. There are various other ways to eject a disk, but the point is that you never do so by pushing the Eject button on the disk drive itself.