I have a inverter which output 220vac but on one wire. I need to connect to a normal 220 plug which has 2 wire each at 110 to get 220. How can I do this. Do I need a transformer

Not going to happen. Your inverter sounds like it has a stardard european type 220vac output... but you need an American style which is actually two 110V legs sharing a common return. Not the right type of output.

You did say inverter....not transformer. In which case you don't have a center tap to use (but not all transformers would even have a center tap anyway).

European 220 measures that between the hot and return....American 220vac only measures that between the two hots , but each individual hot to ground is only 110vac (nominal)

220 is 220 is 220...
Why are you using an inverter? And are you in the USA?