To become a Virtual assistant you'll need to look for companies that are hiring for the virtual assistant positions.
Basically a virtual assistant job could be doing just about anything a company needs you to do. The only difference is you won't be working in their office but instead you'll be working from home or anywhere else from your own computer.
That's what a virtual assistant is. You work remotely for the company instead of commuting to an office.
Look on job websites to find out if there's some companies hiring for remote work and virtual assistant jobs.