Generally two ways, rotary (motor - gen) and statically (like a UPS or VFD but not a VFD).
If it is for occasional and intermittent use, the rotary type will be foolproof and hardened - durable. For extensive use where energy efficiency is a concern, the static frequency converter may be more efficient.
If you are looking at a static type, make sure the load will like the static type output, depends on the load. A motor or transformer load will not be fussy, but another electronic conversion type power supply may or may not match well to the first static converter's output, circuit topology.
I'm sure there a better answer on this board.