How to build a ROS package

$ source /opt/ros/indigo/setup.bash
$ mkdir -p ~/catkin_ws/src
$ cd ~/catkin_ws/src
$ git clone https://github.com/ros-drivers/velodyne.git

Install all the dependencies:

$ cd ..
$ rosdep install --from-paths src --ignore-src --rosdistro kinetic -y

Then, build everything:

$ catkin_make

$ source devel/setup.bash

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How to update workspace packages
$ wstool set metapackages/perception --git https://github.com/ros-perception/vision_opencv.git -t src
$ wstool update -t src