If you've worked in an office before, you can be a Virtual Assistant.
It's a secretary, clerk, office worker who is working "virtually" online. You are hired by an online business, do the work via the internet, and make an income. You work from home. Right?
You simply work from home, doing jobs for online business owners. Sometimes you contract with one person for a specific number of hours per week, for years. Sometimes, you prefer to do all short-term freelancer type jobs.
Like any other home business... it's up to you to determine what you'd like to do with your business.
Teresa works in IT, and started a Techy VA business online called TCM Website Design. She does more technical VA jobs... can you do this too?
Tishia is a VA I met at a Blogging Conference... check out TishiaSavesTime to see what she does for clients.
This link is a Fiverr.com page with all Virtual Assistants to see the variety of work they will do.
You might want to specialize in one field... there are lots of VA's out there seeking work. You might know one field well, already, or you might take a class or two and get the knowledge you need.
I hope this helps you. Being a Virtual Assistant is just like working locally at a business -- only you work from home, and communicate via the internet (email, skype, google, whatever!)