One of the glorious things about living on Kaladesh is the modern marvel of mass production. Fabricate is a new ability found on some creature cards that offers you a choice when that creature enters the battlefield.
As you can see on our friend Glint-Sleeve Artisan, that choice is as follows: put a number of +1/+1 counters on the creature, or create a number of 1/1 colorless Servo artifact creature tokens. The number after fabricate tells you how many +1/+1 counters or Servos you get.
The fabricate ability triggers when the creature enters the battlefield, but you don’t choose counters or tokens until that ability resolves. That means your opponent will have an opportunity to respond to the ability before you make that choice and before the +1/+1 counters or Servo tokens exist. If the creature with fabricate isn’t on the battlefield as the fabricate ability resolves, you must choose to create the Servo tokens. This may be little consolation as your Artisan is dead, but at least you get a little friend in return.
Please see Wizards of the Coast for the complete guide on all things Kaladesh, and from where we got this information.