I would explain it thusly:

People write about stuff that they are interested in.
Other people who are interested in the same stuff, read it, vote on it and comment on it.

This activity has value, just like the hours that you spend at work have value.

The more people like what you write, the more money you make, just like if you worked more hours you would get paid more.

The money for this comes from the North Pole and is made by Santa's elves during the off season when they are not gearing up for Christmas. This explains why there was a lot of it about in June, but not much around now.

Make sense?