The bulb is rated 60 watt. What does it mean?​

The rating 60 Watts means that the bulb will consume 60 Joules/sec and convert it into heat and light. Power = Voltage x Current. If the power supply is 120 Volt (It is usually 110–120 V in the US), then a current of 60/120 Ampere or 0.5 A will enter (and leave) the light bulb.