make robot move in square using base_link?

edit

Hello. Below here I have the code from http://wiki.ros.org/navigation/Tutori....

typedef actionlib::SimpleActionClient<move_base_msgs::movebaseaction> MoveBaseClient;

int main(int argc, char** argv){ ros::init(argc, argv, "simple_navigation_goals");

//tell the action client that we want to spin a thread by default
MoveBaseClient ac("move_base", true);

//wait for the action server to come up
while(!ac.waitForServer(ros::Duration(5.0))){
ROS_INFO("Waiting for the move_base action server to come up"); }

move_base_msgs::MoveBaseGoal goal;

//we'll send a goal to the robot to move 1 meter forward
goal.target_pose.header.frame_id = "base_link";
goal.target_pose.header.stamp = ros::Time::now();

goal.target_pose.pose.position.x = 1.0; goal.target_pose.pose.orientation.w = 1.0;

ROS_INFO("Sending goal"); ac.sendGoal(goal);

ac.waitForResult();

if(ac.getState() == actionlib::SimpleClientGoalState::SUCCEEDED)
ROS_INFO("Hooray, the base moved 1 meter forward");
else
ROS_INFO("The base failed to move forward 1 meter for some reason");

return 0; }

This code is just to make the robot move forward 1m but how do I make it move in a 2m by 2m square? I wanted to use this code as an outline for achieving this goal but I don't understand base_link. I wanted to make it go in a ccw square starting from the bottom left and ending facing the same way it started. I try to use goal.target_pose.pose.orientation.y but it just makes the robot spin in a circle. I tried to use it like this...

goal.target_pose.pose.position.x = 2;
goal.target_pose.pose.orientation.w = 1.0; goal.target_pose.pose.position.y = 2;
goal.target_pose.pose.orientation.w = 1.0;
goal.target_pose.pose.position.x = -2;
goal.target_pose.pose.orientation.w = 1.0; goal.target_pose.pose.position.y = -2;
goal.target_pose.pose.orientation.w = -3.14;

but it didn't work. Help please!