You need an external 12V DC power supply if you want to drive 12V LEDs.
The outputs on a 1012 are solid state switches to ground, so you need to wire each LED up as follows:
- ground of 12V supply wired to G terminal on 1012
- positive wire of 12V supply to LED anode
- LED cathode to digital output (0-15) terminal on 1012
Then you can repeat by wiring other LEDs in parallel to different outputs. You don't need to run a new ground wire for every LED you add because all of the grounds on the 1012 are tied together (but keep in mind that the current of all active LEDs are going through that wire so you may want to run a few extras depending on number of LEDs, the forward current, and the gauge of cable you're using).