Can I plug my gererator into the 220 dryer outlet and back power my house if I shut off the main breaker at the panel, when the power goes out?

Can you? Yes. Is it legal and safe? NO! Buy a transfer switch and do it properly.

Where do I get transfer switch and do I need an electrician to wire it into the panel?

Where do I get transfer switch and do I need an electrician to wire it into the panel?

Yes, you should hire a professional and request an electrical permit and inspection by the sub-code official to verify an appropriate installation.

I will reiterate, extremely dangerous to do this with out transfer switch and proper wiring. You could get some one killed should you fail to disconnect main breakers and cause a fire when power is return from grid. To make such a connection, even if you turn off main breaker, requires using a "suicide" cord, which is a cord with a male plug on each end. That means exposed electrodes on each end, which can kill you.

Edit for emphasis on the danger of doing something like this.
Think about this. The power coming down the street to the transformer is probably 5000 to 7000 volts, where it is stepped down to 120 volts to your home. Should you "accidentally" send 120 volts back up the line, it will be stepped UP to the 5000 to 7000 volts by the same transformer. Do you want to be a linesman?

Got it, a guy from work said it would be okay. I had my doubts and you guys have confirmed them. Thanks for the info.

Got it, a guy from work said it would be okay. I had my doubts and you guys have confirmed them. Thanks for the info.Unfortunately many people (with no clue) will tell you it is OK. It is not!