Price comparing methods for a newbie

[Benjamin Barredo]

Hello,

I'm doing my homework and soaking in my first real estate investment book "The Book On How to Invest in Real Estate With Little Or No Money Down" and a question comes to mind. 

You find a fixer-upper, bit how do you know it's a great deal without knowing what it is worth? 

I know part of that answer is analyzing the property but one must also know the worth of similar homes in the neighborhood. Where do I go to get that information? Is there a website? Do I hire am agent (I'm not financially there yet)? 

Help a brother out, please.