I have a leviton 057 with 2 black wires and 1

http://www.automanualparts.com/wiring-diagram-for-3-way-switch-with-dimmer/

use above link

Connect the green dimmer wire to your ground wire

with a three way switch like this, you will have two traveller wires and a common wire. Look in the instructions for the switch or on the back of the device itself to see if there is a wire labeled "common" or "com". This common wire from the old switch hooks up to the common wire on the new switch. I did a bit of searching on the leviton 6602, but couldn't find anything specifically about the three way version (I would venture to guess, however, that the red wire on the old switch is the common). The common on one of the three way switches will always be a constant hot (or power) wire...the common on the other three way switch will be the "switch leg" or the wire that connects directly to the light. The two travellers go to the other two wires. Check the pamplet that came with the lutron device, it should show which wire is common and which are travellers.

You cannot wire dimmers in series and expect circuit to operate.
Problem is not 100% clear. Add a comment and include more information.

1) You have 12 dimmers.
Each dimmer has 2 black wires and a green ground wire.
The 2 black wires tell electrician that the dimmer wires are reversible.
One black dimmer wire connects to Hot from breaker, and the other black wire connects to wire going to Load (halogen lights).
If power passes through each dimmer going to next dimmer, the circuit will not work.

2) Unknown what you are replacing. Are you replacing 12 switches with 12 dimmers? Or maybe replacing 1 switch with 12 dimmers.
Number and type of devices being replaced is not known. And wires to each of these dimmers is not known.

3) You have a single 14-2 wire going to all 14 dimmers? Or does each dimmer have a different 14-2 wire?

4) You want to wire dimmers in series? So you want power to flow through one dimmer and control next dimmer?
You cannot wire dimmers in this manner and expect circuit to operate.
You can wire ordinary switches in series, but not dimmers.

5) Typically dimmers and switches are wired in parallel.
The Hot wire connects to one wire on each dimmer.
Since your dimmer has 2 black wires, the hot connects to either black wire on dimmer.
Then a jumper wire is added to connection, and the jumper wire carries power to next dimmer, and so on.
In this manner, each dimmer receives 120V potential. And then wire going to load connects to other black wire on each dimmer.

One black is will hook up to one of the black wires inside the switch box in the wall and the other will hook to the other black wire in the box, The green will connect to the bare copper wire which is the ground wire.

one of the white wires has power on it constantly....that wire connects to the black wire of the leviton.......the other white wire which has no power to it is going to whatever needs power so that wire connects to the red wire of the leviton....the green wire connects to the metal box where your mounting the leviton.

i want two dimmer switch parrel they both fhave two black and one green how fo you wire it up

You are correct in assuming green is the ground and connects to bare copper wire. Black is always the HOT wire and should be attached to the black wire. Red wire connects to white wire.

one black from the dimmer to black. the other black from the dimmer connected to red. the green connected to the bare wire.

hook up the red to red
black to black
green to bare wire
tie white wire to other whites in back of switch box in the wall.
If no whites in there cap it off with a wire connector.