Electrical question?

[JERRY2KONE]

Below is a LINK that shows a similar appliance which in the specs shows 208-240v power supply.

http://www.curtos.com/products/Gener...sa2201rss.html

The microwave that was ordered may be this one or one very similar. The out of phase legs sound a bit strange to me. So from what some of you are sharing if you want to hook up a new welding machine in your garage you have to have two 120v legs to supply power and both legs have to be out of phase, correct? I have never heard this before. The second part of this question is how do you get or even know that these legs are out of phase when you hook it up? And why would they have to be out of phase?