bitcoinica is margined trading. i.e., not for noobs
here's probably the best place to go to start learning: http://www.finra.org/Investors/SmartInvesting/GettingStarted/OpeningaBrokerageAccount/index.htm
fortunately, bitcoinica does not limit access and does not send guido after you if you lose more than you deposited with them. there is no penalty to trading even just tiny amounts so you can give it a try with just a fraction of a bitcoin if you wish.
by default your margin level is 2.5:1. you can update your profile to get to 5:1 or to 10:1 even if you like losing your money instantly.