Can somone PLEASE tell me how to use the diff drive plugin?????????

So I am very new to gazebo, working on my first project. So far my program spawns robots randomly in a given area. I want to be able to control them via a ROS node. Since Im using Pioneer2dx models, I am trying to use the diff drive plugin. I have spent literally days trying to find relevant information online, to no avail. I have also posted multiple forum questions on here and got answers that either didn't work or weren't useful to me. Here's what I REALLY need to know: 1. How to access the diff drive plugin from my code (what is the #include). 2. What functions do I need to use to get the robot to move in the simulation 3. How to link this plugin to my pioneer2dx model in the world file. Please help! thanks in advance. . . --------------- ## UPDATE## Here is my world file: model://sunmodel://ground_planefalsemodel://pioneer2dxtrue10left_wheel_hingeright_wheel_hinge0.53800.241020cmd_velodomodombase_footprintgz0 0 0 0 0 08 8 0.01random I get this error when i try to open the world file: Launching simulator. . .done
Warning [parser.cc:437] Converting a deprecated SDF source[data-string].
[FATAL] [1468348607.233504158]: You must call ros::init() before creating the first NodeHandle
Couldn't find an AF_INET address for []
Couldn't find an AF_INET address for []
[ERROR] [1468348607.237102184]: [registerPublisher] Failed to contact master at [:0]. Retrying...
Couldn't find an AF_INET address for []
Couldn't find an AF_INET address for []
Couldn't find an AF_INET address for []
Couldn't find an AF_INET address for []
Couldn't find an AF_INET address for []
Couldn't find an AF_INET address for []
Couldn't find an AF_INET address for []
Couldn't find an AF_INET address for []
Couldn't find an AF_INET address for []
Couldn't find an AF_INET address for []
^CCouldn't find an AF_INET address for []
why would my world file be giving me an error to do with ros::init()?