Tutorials
Now, to test your installation, please proceed to the ROS Tutorials.
Obtain source code of the installed packages
If you know the location of the repository of each package, you know you can obtain all the code there. But it's often hard even for experienced developers to reach the correct maintained repository of certain packages. Also, in some situations you just want to get the source of the released, installed version of a package. The methods described here the best for these cases.
In earlier days of ROS (supposedly electric or earlier) you can obtain by the way noted in this question.
Now just apt-get source (sudo not needed) as following. You don't even need to explicitly specify deb-src entry etc. This downloads from the server all the files in the released version of the package (i.e. things not installed in the installation rule (e.g. CMakeLists.txt) are also included).
$ apt-get source ros-hydro-laser-pipeline
Drawback might be that you have to specifify a single, exact package name (asterisk doesn't work).