So, a very easy, educative and cheap way to start paper trading is by going to www.thinkorswim.com and then go to "Software --> Paper Trading - Paper money" so you can create your virtual account and download the software package. Install the package on your PC and log in using the account credentials you just created on their web site. If you live in Canada then you can go www.thinkorswim.ca and do similar. On their website you can also go "Software --> Desktop - thinkDesktop", that's just another way to download the software and create your account. Once set up, you can go to the help tab, or alternatively the learning center at http://mediaserver.thinkorswim.com/support/learningCenter/tos_learningcenter.html and start watching the video tutorials on how to use this powerful tool.
So that's it!! A free way to start learning and practicing with one of the most powerful tools nowadays!