If all you have is single-phase 240-volt current and you need 480-volt three-phase current, you can step the voltage up to 480 volts using a transformer. Once at 480 volts, the single-phase current must be converted to three-phase using a phase converter. Rotary phase converters use an electric motor with capacitors to generate two additional phases of current, while static converters use electronics to do the same thing. One possible application is running three-phase motors on shop equipment at 480 volts.
Single-phase power is suitable for small household appliances, but because each voltage cycle sees the power drop briefly to zero, three-phase power is required for heavy electrical equipment. In three-phase power, the power output is constant. Single-phase to three-phase converters are available.