what is the best path for a really beginner

Im a beginner in javascript and node.js.

I have some knowlegde about ruby and rails.

I have tried to learn node.js by using the lessons of nodeschoo.io but the exercises were something too difficult and too abstract

Now I wonder what is the best path to learn node.js with as ultimate goal making a sort of ecommerce site for a toy library.

There's a lot of options -- https://github.com/rockbot/node-for-beginners has a great list of places to start learning, much of it web-focused. You might have to ask more specific questions, though, since node.js in general is very broad.

You can learn interactively with this one, a lot of coworkers already has been started with codeschool:

https://www.codeschool.com/paths/javascript