XKCD has a comic called Up Goer Five - which is a comic that describes all the details of what I'm guessing is a Saturn V rocket... but only using the set of 1000 most commonly used words of the english language... it ends up pretty funny :)
and now he's also released an upgoer5 text editor that lets you try to write anything, so long as it is using the "ten hundred" most commonly-used words.
Here's my attempt at describing what I do for a living:
There is a place where lots of computers are joined to lots of other computers. You can put words and pictures there that other people can read. There are groups of people that like to make things that other people can buy. These groups get me to make words and pictures that look pretty, to let other people know about the things their group makes. Then, people with computers can come to the place with lots of computers joined together. They come and look at the words I wrote and the pictures I put with the words, and decide if they want to buy the things the group made.
It's more difficult to be clear than you might think...