All reasonable advice from others below I reckon, and the best is undoubtably  not to stuff around with it it you don't really know what you are doing - and having to ask the question suggests to me you don't really.

A couple of thoughts that might help to safely narrow down where the problem lies;
- the fact that it's tripping so regularly should make finding it fairly quick and easy.
- isolate each circuit by turning off individual breakers to the power circuits until the circuit that has the fault or faulty device is found. When circuit with fault indentified then remove plugged in devices to isolate which is faulty, if it is a faulty device and not the wiring.
- you can buy little gpo (powerpoint) testers that have three ligths on them and you plug them in and turn on - different lights will indicate a wiring fault at the power point
- in NSW (don't know about other regions) light circuits are not normally put through an earth leakage breaker
- electric water heater are not normally put on earth leakage either and depending on age of installtion it was typical to not put fridge circuits on, nowadays it is more typical to put fridge on
- it could also be a faulty eath leakage breaker - the test button circuit does actually set up an earth leakage
- an electrician will quickly and easily sort this and can do an insulation resistance test on the whole house

All up get the sparky in to check and provide peace of mind - crazy not to.