While it is important to call a licensed electrician if you are experiencing regular tripping of your safety switch, there are some simple things a householder can do in a one-off situation.
If just one of the circuit breakers has tripped, that indicates an appliance on that circuit is faulty. For example, a toaster or kettle. Disconnect it and reset the circuit breaker.
If the main safety switch is tripped, try unplugging every appliance from every wall socket around the house and reset the switch. If it trips again, go around every room and check that you actually disconnected or turned off every appliance. This includes fridges, washing machines and even the stove range hood.
When you reset the safety switch and it doesn’t trip, slowly and thoroughly reconnect all appliances until you discover the one that is tripping the safety switch.
If the safety switch has tripped with a spark-like flash or made a loud cracking sound, don’t touch it! This indicates a more serious overload issue. Call a licensed electrician immediately.