I'm picking up used Antminer S3's on ebay,about $125+ shipping.Most can be underclocked later,be sure to ask about the underclocking,I hear some can't be 
So how doe sit work if I invest in several of Antminer S3's?
Do I connect it to my desktop somehow?
Does it have an Operating System?
How do I buy one of those, open the box, and start mining bitcoins?