I'm new to Mac and have a stupid question.

How do I get the disk drive to open in my MacBook Pro? Maybe I just slide a disk in, but if that’s the case, how do I eject the current disk? I don’t even know if there is a disk in there but the new disk does not want to go in so I’m assuming its already occupied.
I know I’m going to love this but the learning curve is a killer for this old broad.