Mike123. PLEASE take Ray Galea's advice and get an electrician in.
It's very simple to do what you need but you just do NOT have enough knowledge to be SAFE.
You can't smell it, can't see it but when you feel it, it's too damn late. Electicity KILLS.
Thankfully you don't have the loop in to your light switch but the switch drop will be LIVE.
A light switch is just that, switches the light (LIVE) so doesn't have a neutral.
L1, L2, C, indicates a 2 way switch, it changes contact between C (common) and L1, L2.
If it's in a metal back box then it should have and earth terminal, some plastic ones do but not often.
IF a Neutral is present it'll be in a loos terminal block.
Dare say you're a clever guy but this is not something to learn on without hands on expert guidance, you could kill yourself or your partner or children.
Please, Please call a sparks.