Chemical Changes Stress or joy chemical changes happen.
Structural Changes The same thing keeps happening over time there will be structural change.
Functional Changes Serving the purpose.
Automated Changes Then everything becomes automated through practice.
Example:
Starting to ride a bicycle there will be joy, fear and stress. These all start giving you the chemical changes in your brain. Releasing certain chemicals.
With time the different structures e.g. neurons start firing, connecting with each other more strongly.
Once the functional stage happens and finishes then you don't have to bother much about how to ride a bicycle.
Things become automated you will not even think of where you are going. Automatically hands go in the right direction legs start pedalling it becomes automatic.