Hi guys. I just started delving into reverse engineering so I am far from the authority on the field, but I wanted to share a cool website I found which helped me very much to grasp the concepts. It's essentially series of reversal challenges which are done in interactive debugger on the webpage, with nice little (but optional) interactive tutorial. All in all it serves nicely to familiarize with the debugger and fundamentals.
Afterwards, I suggest you to take a look at the challenges on site bellow if you need something more challenging