Electricity is delivered to end users via distribution lines.
Typically, a household as well as most commercial / institutional and many industrial customers use electricity at 120 or 240 volts. However, power enters the distribution sytem at much higher voltages (upwards of 72kV). It therefore needs to be reduced to a safe level for consumers (although some very large users take supply at high voltage).
Step-down transformers are used to do the deed. The transformers come in various shapes and sizes. The biggest ones are housed in substations, a familiar sight to everyone. Smaller transformers reside in little grey boxes or on top of power poles.