On your workstation, install the robot simulator Gazebo only if you plan to work with a simulated MiRo robot. If you plan to work with physical MiRo, you do not need the simulator.
There are many web resources that will help you to, but you should read the notes here before you proceed to ensure you install the correct version.
Do not install
gazebo7 package, because this is not updated regularly. Instead, install
ros-kinetic-gazebo-dev which provides the version that marries up with your ROS installation (at time of writing, Gazebo 7.14.0).
Restart your bash prompt and you should now be able to invoke the simulator as follows.