Warning: 3D pictures are ADDICTIVE. You will find yourself spending a lot more time appreciating the simplest snapshots. Next thing you know you'll be browsing ebay for old stereoscopic equipment, blathering on at dinner parties about how much better 3D pictures are than "flat" photos, and spending your weekends making weird stuff to post on Instructables. Read this at your own peril.
Step 1: Buy the parts...
They cost $24 each (plus $10 shipping) and arrive within a few days.