I take it this is a side project then ? Well ROS only deals with communication between different software and middleware components. If you need a physical simulation for your robot and want to be able to switch between controlling the real robot and it's simulated counterpart the Ros + Rviz + Gazebo software packages is what you will want.
Gazebo is a physics simulator, which is meant to represent the real physical world with your robot. A good Gazebo tutorial here shows how to control a stick robot with a camera and IR sensor.
For ROS it is much easier there are plenty of good tutorials such as the turtle bot ones: http://wiki.ros.org/ROS/Tutorials/Und... .
Rviz is a visualisation display, it is to show you the state of the robot and all sensory information available. You use this both when you are running your simulation in Gazebo and when you are running the real robot.
What kind of robot and what task are you considering to do ? From ardigos we page it seams they specialize in hardware devices. I would need a bit more details to give you a clean answer.
just as same as industrial robot like kuka or abb. it will have its own processor for working, teach pendant and a computer for simulation. however, i want the simulation both in realtime as well as in offline mode. for it i'm trying to understand which software should i follow first. i searched....
.....alot and found ros can be a way. now the problem is i'm from mechanical background,so dont have much knowledge of ubuntu but i love programming and interested to do it myself. obviously, i dont have much knowledge of microcontrollers, so i decided to go for arduino.now the basic question is....