There are a couple of different ways you can print out multiple photos on your Mac. The first is through iPhoto, which is the bundled photo program for the Mac operating system. You can pick photos out of the iPhoto library or select an entire album that you have created for an event. If your photos are not in iPhoto and you don't feel like importing them, you can print them using Preview, the default program on the Mac for viewing images like JPEGs you download or share with friends.
Open iPhoto and select the images you want to print using the Library (located in the sidebar) or choose an entire album from the sidebar. To pick individual images, hold the "Command" key (it has a cloverleaf on it) and click on each photo.
Choose "File" from the top menu and then "Print." Make your print selections. You can print one photo per page or print multiple images on the same page using the Contact Sheet option. You can also control the border options and pick your paper size.
Click "Print" to confirm your choices and print the photos.
Click on each of the photos you wish to print while holding down the Command key. It is easier if they are on the desktop or in the same folder.
Click in "File" and then "Open with" from the top menu. Choose "Preview."
Highlight each of the photos by clicking them individually. You can also use the "marquee drag" technique by clicking and dragging over all the photos in the sidebar to select them all, or press "Command" and "A".
Click on "File" and then "Print selected images" from the top menu.
Select how many images you would like per page using the drop-down menu at the bottom of the print pane. Select your other print options such as paper size and orientation, then press "Print."