A practitioner is an expert who uses that knowledge as part of a profession. Every yoga practitioner started by attending an introductory class.
In practitioner, you can see the word practice, which everyone says will make you perfect. Practice can also mean the clients, daily activities, and location where a professional such as a doctor works. So a practitioner is someone who has learned everything about his or her field and is actively working in that field. So don't worry about going to the doctor — you won't be practice for this practitioner.