A generator is not required, but you can use a generator to power your 220V MIG welder. The generator will only be necessary if you don't have a 220V network in your workshop or wherever you're carrying out the project. The generator provides power to your welder without needing the mains.
If you need one, you can simply purchase a welder generator suitable for supplying 220 volts. Asides from giving power to your welding machine, you can use them for other lights and tools. They also come in handy as a backup power source if you lose electrical power.