You can get to this link for more information: http://wiki.ros.org/ROS/Tutorials

What is ROS ?

The Robot Operating System (ROS) is a set of software libraries and tools that help you build robot applications. From drivers to state-of-the-art algorithms, and with powerful developer tools, ROS has what you need for your next robotics project. And it's all open source.

ROS Package

For a package to be considered a catkin package it must meet a few requirements:

• The package must contain a catkin compliant package.xml file.
  • That package.xml file provides meta information about the package.
• The package must contain a CMakeLists.txt which uses catkin.
  • If it is a catkin metapackage it must have the relevant boilerplate CMakeLists.txt file.
• Each package must have its own folder
  • This means no nested packages nor multiple packages sharing the same directory.

The simplest possible package might have a structure which looks like this:

my_package/
  CMakeLists.txt
  package.xml

To buliding a ROS package, we use:

$ catkin_make [make_targets] [-DCMAKE_VARIABLES=...]

Quick Overview of Graph Concepts

• Nodes: A node is an executable that uses ROS to communicate with other nodes.
• Messages: ROS data type used when subscribing or publishing to a topic.
• Topics: Nodes can publish messages to a topic as well as subscribe to a topic to receive messages.
• Master: Name service for ROS (i.e. helps nodes find each other)
• rosout: ROS equivalent of stdout/stderr
• roscore: Master + rosout + parameter server (parameter server will be introduced later)

ROS Nodes