- Select the photos you want to print. Command-click to select individual photos or Shift-click to select a range of photos.
- Go to File / Print in the menu bar.
- In the left pane, leave Standard selected or choose one of the other options.
- Change "Print Size" to a standard print size or set to Custom... to set your own size.
- A few more customization options are available if you click the Customize… button.
If you want to print multiple copies of the same photo on one page, check out this tip.
If you want to print photos from iPhoto at a photo lab like Walgreens or Walmart, check out this tip.