That instance variable called age is being created to hold a detail of any Dogs that we create.
That is defining the constructor that will be used every time we create a new Dog. It will be expecting a value, a parameter called dogsAge, to be sent in when a Dog is created. The parameter will be an integer.
There we are assigning the value of the parameter to our instance variable.
That is how we create a new Dog. It will be called spike and it will have a dogsAge of 17.