The name Ziti comes from the word "zita" which means "bride" because it was traditionally served at weddings. Ziti pasta (traditionally) are long thick tubes that are broken into pieces before cooking. In the U.S. ziti are tubes that are about 2" long although you can find imports of the longer pasta.
Ziti pasta can be purchased at well-stocked grocery stores although it can be difficult to find in some regions of the U.S. A reliable brand is Barilla and it can be found on Amazon.com Ziti, Barilla if you can't locate it locally.
You need to cook Ziti for about 11 - 12 minutes in rapidly boiling water for "al dente" pasta.
If ziti is unavailable then there are several very good tubular pasta substitutes including: