1)Two way switches are Not a ON/OFF switch like 1 way switches.
2)It is 3 pole switch Has C-L1-L2 on both switches.
3)Two way switches are always come like "sakalathis" for a bulb,fan,Etc...
4)If that two SAKALATHIS(switches) are in same mood either (BOTH ON or BOTH OFF) bulb turns on.
5)If any one SAKALATHI has Different mood . It will not allow the BULB to do his work. SIMPLY no light (DARK)
6)If u want wiring details.I will DRAW and explain in same way.