(Urgent) Dimmer switch wiring question

[Tall Paul]

Hello all, just a simple question for those that know what they are doing!

I have a dimmer switch with L1 L2 and C terminals.
The cable coming out of the wall has earth, red, and black with a red sleeve on it. I know where the earth goes but what about the other two?

BTW, the instructions say 'don't connect to the neutral side of the mains' and 'L2 will have no connection in a one way dimmer'

Thanks!

[ericmark]

Red to C and Black with red sleeve to C1 and C2 not connected.