Second switches are a common feature of houses with stairs, for large rooms that have more than one entrance, or for the master bedroom where the main lighting can be switched on as you enter and turned off bedside as you kiss your partner goodnight. Installing a second switch for one light is a job that involves new 3-core and earth cable and new 3-way switches. You should do it only if you have some experience of working with electrical house wiring.
Go to the point where you wish to install the new switch. Either install a surface mounted 3-way switch and self-adhesive conduit to run from the new switch to the skirting board or, for an invisible finish, fit a new internal switch box and conduit into the wall plaster using a hammer and chisel. Both mountings will require a drill, raw plugs and screws. Turn off the electricity at the mains and go to the existing single switch.
Unscrew the switch and look at the wiring. You will find three wires, commonly referred to as "2-core and earth." The red or brown wire is live. The black or blue wire is neutral and the green or green and yellow wire is the earth wire. As nearly all houses have electric cables that run the live circuit from the consumer control unit to the nearest lighting point then on to the next and so on, the cable you are looking at has come down the wall from your main room light.
Undo the wiring connections, discard the switch and replace it with a 3-way switch. A 3-way switch takes a 3-core and earth cable. It has a connection for the earth wire and connections for the live and neutral wires called L1 and L2. The final connection is called a "common." Rewire your existing live and neutral wires into your new 3-core and earth switch. They connect to L1 and L2 and it doesn't matter which goes where as this only dictates the up/down way the switch works.
Take a new length of 3-core and earth cable long enough to reach your new switching point. This 3-core and earth cable runs from the existing switch, via a surface conduit or internally within the wall, down to the skirting board and around the room to the new switching point. Tack the new cable neatly into place along the top of your skirting board with cable tacks.
Connect the red and blue wires of this new cable to L1 and L2 and connect the yellow cable to the "common" at both the original and new switches. You will end up with two sets of live and neutral wires, a common and an earth in the original switch, and one set of live and neutral wires, a common and an earth in the new switch. Finally, make good your decoration and the job is complete.