To get a fast good overview of the basics of Ruby on Rails. The very famous beginning for new commers is definitely the wonderful Code School, Rails for Zombies. Like all Code School courses, it is fun to work and help you retain what you have learned by doing little code snippets assignments after every chapter! With this tutorial you build a a small web app similar to Twitter. That was an excellent start for me.
In case you get stuck at an exercises (most are easy and straight forward), just google : rails for zombies lab (Number) exercise (Number) and you will find the answers. Most are in stackoverflow.com
Please if you fail with one exercise, try more. rewatch the video of the chapter, if you still could not insert the right code, only then google the answer. I needed to google only once.