If you're interested in learning to use ROS, I've just put together a tutorial to help some of the people in my lab that may help you get started too!
The tutorial is intended to help you get up to speed with how everything is connected together in ROS. Once you've gone through each section, you should have the base-level of knowledge needed to work with the huge selection of ROS packages that are out there and really speed up your robotics development.
You can find it over on my github: https://github.com/aransena/kcl_ros_tut/
You'll need Ubuntu 14.04, which you can either install on a separate partition on your computer, or run in a virtual machine. If running in a virtual machine, I recommend using the ROS Indigo image from Nootrix (linked in the tutorial) as it has everything you need to get started pre-installed!
If you think I've forgotten anything important, or something isn't clear, do let me know.