- Go to File > Print (or Ctrl+P)
- In the settings, look for where it says "Full Page Slides: Print 1 slide per page." Click on that.
- Choose the layout you want. The "3 slides" option will add a column of lines for your audience to jot in their own notes easily. The other layouts are just the slides.

Colors & Background
An optimal printed slideshow is going to look different than one optimized for an actual presentation. Even if you want to print in color, it can still be harder to read the slide content when it's shrunk down, and a grayscale version of a colored background will make that more difficult.
At the very least, swap the "Color" setting in the Print menu to "Black and White" instead. Better yet, save a separate version of your presentation with a plain theme to remove the background colors. Go to Design > then select the first, blank/white theme.

Double-check that your slides still show all the info you want and maybe remove non-essential decorative images. Save as a separate copy, then follow the instructions above to print multiple slides per page.