Many people makes a mistake by calling a 3 Gang Switch with 3 Way Switch. For a person not familiar with the electrical terms, it is forgivable. The name does seems very appropriate if you look at the switch. It has 3 switches lined up side by side and naturally many people will call them 3 way switch. The problem is so common that many have ended up buying the wrong kind of switches.
The fact is these switches looks and works very differently. The most distinct difference is a 3 gang Switch HAS 3 individual switches lined up side by side, WHEREAS, a 3 way switch is only ONE switch. It is called a 3 Way Switch simply because it works three ways. As described before, the 3 Way Switch is a switch which is normally located at the center point of a long corridor so when someone switches on the corridor lights from either ends, another person can switch those lights off if he is in the middle of the corridor. It is just for convenience sake.
The 3 Gang Switch on the other hand are just normal switches we see in our homes. They are individual switches bundled together so it looks neater and save space.
The wiring installations for both these switches are also differently done. Where the 3 Gang Switch is a straight forward installation, the 3 way switch need some extra wires like those described in the installation of a 2 way switch. Only this time, the common wires will have to go through the 3 way switch first.