If all you need is to add an Edge with a Description, and you're not worried about making sure pre-requisites are met or having any changes that Edge might implement directly onto a character sheet, then using the Editor just for that is really easy. Just go to the Edge tab, hit "New (Blank)", Type in the name you want or your Edge, make up a unique ID (you might want to use some little 2-letter identifier for your House Rules, like HR, in the name, just to help make sure you don't end up using the same identifier accidentally... so let's say you had your own version of Alertness you want your players to use, well there is already an "edgAlert", but if you called it "edgHRAlert" you won't run into any problems.) Next put in the "Sumarry Text", that's what will show up on the PDF character sheets. Then you can put in your detaild description and you're basically done. The detailed won't show up on the PDF sheet, and you'd have to mess with the custom sheet stuff to get it to print out otherwise, but at least from within the Hero Lab it will show up if you're mousing over it and such.
If you want to do some of the basic pre-requisite stuff, like set it to requiring "Novice" Rank or calling it a "Background Edge" then some of that stuff is down under the description box for selecting. For a one-shot game, I don't know that I would bother with any of that, though.
Now if you want to start playing around with having your Edges modify Traits in some way, or have a bunch of pre-requisites that it will warn you about if the character doesn't have... that's a whole other ball game. Some of us are figuring it out more and more, though, so maybe we can help you there if you start getting stuck trying to get into the more detailed stuff. But for basic stuff, it's actually pretty quick to set it up.
If you have some of the other setting files already loaded and you try to do a new Edge with "New (Copy)", just be aware of the button at the very bottom of those called "Sources". If any of the sources in the list that brings up are checked then your new Edge will also only show up in the program if your "Configure Hero" settings also have that setting checked. For one-shot's I would just make sure you don't have any settings checked and those will just show up no matter what setting you use. If you want to use them more permanently then make up a setting for them and put those in there.
Hope that helps (and isn't too convoluted. :/)
