The LOOPING terminal is used to connect the EARTH wire.
The COMMON terminal is used to connect the NEUTRAL wire. (Sometimes labelled C on other switches).
The 1 WAY terminal is used to connect the LIVE wire when used as just a 1 way switch. This means there is only 1 switch to control the lighting circuit. (Sometimes labelled L1 on other switches).
The 2 WAY terminal is used to connect other switches in a circuit with more than one switch controlling the lighting circuit. (Sometimes labelled L2 on other switches).
If in doubt, always consult a qualified electrician.