Do working as a lift driver means that I am a self employed?

Yes, being a driver for Lyft does mean that you are self-employed. When you're a driver for a ride-sharing company such as Lyft or other car sharing service, the most important thing to understand about your taxes is that you are probably not an employee of Uber, Lyft or Sidecar. 

Drivers for these companies are usually independent contractors, a fact that has tax implications, both at filing time and year-round. Uber Income is considered self employment income and you have to complete a Schedule C which is found in TurboTax Home and Business (desktop) or TurboTax Self-Employed (online).

Being an independent contractor means that you're self-employed . As far as the ride-share company is concerned, you're the owner of a separate business that it uses to provide driving services. So when you receive a payment, understand that it's not a traditional "paycheck," and likely no taxes have been taken out.

TurboTax Home & Business (desktop version)  https://turbotax.intuit.com/personal-taxes/cd-download/home-and-business.jsp 

TurboTax Self-Employed  (online version)  https://turbotax.intuit.com/personal-taxes/online/self-employed.jsp