Duplex printing means printing on both sides of the paper. Whether you need it depends on which imposition style you’re using and how you’ve configured it.
Some imposition styles are inherently double-sided — Saddle Stitch, Multi-Signature, Multi-Up Booklet, Concertina Zine, and Tri-Fold always print on both sides of every sheet.
Others give you a choice. One-Up, Comb Binding, and Business Cards each have a Double-sided printing option in their imposition settings. Turn it on if you want to use both sides of the paper, or leave it off for single-sided output.
The remaining styles — Labels and 8-Page Zine — are single-sided. (The one exception is the 8-Page Zine’s Secret poster back-of-sheet option, which does need duplex.)
You don’t need to worry about remembering all this. Octavo knows whether the current imposition needs duplex, and configures the Print pane accordingly.
If your printer can print double-sided on its own, this is the easy option. Select Automatic in the Duplex section of the Print pane, and Octavo tells the printer which way to flip the paper based on your imposition style and paper orientation. You just hit Print and collect your output.
If your printer doesn’t support automatic duplex — or if you prefer to handle the flipping yourself — select Manual. This prints the front and back sides as separate jobs, and you flip the paper stack in between.
When manual duplex is selected, you get a few extra options:
Getting manual duplex right can take a bit of experimentation. Every printer behaves slightly differently when it comes to which way you flip the stack and whether you need reverse page order. I’d suggest doing a test run with a couple of sheets first.