Administration positions are difficult posts to fill and price for at major firms. Often, extra staff are only needed for specific projects, or for specific periods of time when it's especially busy. Companies end up hiring someone full time, only for them to be sat doing nothing for a couple of days a week, or half their working day. It isn't efficient for the company or the staff.
That's where you can step in as a virtual admin, filling the time that needs to be filled and charging by the hour. You could work for multiple different companies at different points of the week; and doing it all from home. That's one of the benefits of the internet age! You'd be a far more attractive pick for most companies than hiring regular staff, because they don't have to worry about your tax, holiday or sick pay. They just send you money, and you deal with it all yourself.