Start by thinking, “what is the law of conservation of energy?”
The law of conservation of energy states that energy cannot be created nor destroyed, but can be transferred or transformed.
In terms of machines, this means that machines don’t just create their energy to do the tasks out of the blue, they have to have a source of energy.
With machines, they usually have electrical energy (if machines are plugged into a power point) or chemical energy (for fuel etc). And due to the law of conservation of energy the machine turns this chemical or electrical energy into whatever type of energy it has been made to output, for example a toaster gets electrical energy into it and then heat energy gets released to heat the bread!