To practice is to intentionally perform a specific activity.
A practice is a specific activity which is intentionally and repeatedly performed.
Practical is a trait of activities which can be beneficially practiced.
In the context of specialization, to practice is to repeatedly use and (hopefully) develop a skill.
Practice often especially represents using a skill as a component of training. However, practice may also refer to using skills as a component of any role. For example, lawyers practice law and doctors practice medicine.