"how to" on installing a 30 amp plug at your home?

When I installed one- the local Hardware store had an external box with a 30 Amp rv out let- I bought a 30 AMP GFI circuit for my breaker box- and luck would have it the wall I put it on was just below the breaker box on the outside so a 4' section of wire was all I needed to finish it- been there 3 years except the one time I forgot to unplug from it- oops.