How should I start?
Dheeraj already recommended "Agile Web Development with Rails".
That's one good choice. Another is Michael Hartl's "Ruby on Rails
Tutorial: Learn Rails by Example", also available for free as a web
site (at http://ruby.railstutorial.org/ruby-on-rails-tutorial-book/).
There are many others. One important point is to make sure it teaches
Ruby of at least version 1.9.2, and Rails of at least version 3.1.
There are significant differences from prior versions, but learning
the earlier ones can wait, possibly forever.
Also check out the Rails Guides, available at http://guides.rubyonrails.org/.
Once you've read all that, and done the exercises, think up some
simple projects *you* want to do. Then figure out how to do it. Put
it up on Heroku. Share the code on Github. Ask for feedback.
Does it have to be perfect?
Absolutely not. Nothing is perfect. Do your best, and if you get
stuck, ask us for advice.
Should I be forking someone else project and seeing what to do with it
That's one way to go. Once you're at least somewhat confident of your
skills, you can even fork a popular open source project, take a look
at the "issues", and see what you can fix.