hi, new laws and regs say unless you are a competent electrician with certificate part "p" you must not touch it.
anyway. it will be connected to the two terminals in the ceiling fitting that feed the bulb.( one is neutral and one is live from the light switch when it is switched on). you will need to run a piece of 1.0 twin and earth cable from the ceiling fitting to the new fan position(which could be in the loft )with an exhaust tube venting outside. you may have to cut a hole in the plasterboard ceiling, so mark it from the loft so it does not finish up with a joist in the way. the earth wire is MOST important, so make sure it is connected firmly. no wires or electrical switches must be touchable from anywhere in the bathroom, and the switch(existing) should be a pull cord type. BEFORE you start switch off all the power at the consumer unit and try the light in the bathroom to make sure it is dead and make sure everyone is aware that they must not switch on the power. earth sleeving should be put over earth wire to protect and identify it. seperate transformers should be screwed to the joist and not touching anything that may catch fire and not touching central heating pipes or cables.common sense is the word. if in doubt, fit the fan and call in a sparks to do the connections and test.
alf.