When you take a course in NLP, you are awarded a certification that calls you a practitioner. If it said "practicer" would you be more likely to see the connection between practicing and NLP? NLP is not something you learn so you can know it. It's something you learn to practice so that you can do it over and over again.
What is the advantage of practicing? You get better. If you practice NLP, you get better at managing your own state and influencing the states of people around you. That's pretty useful. It means that other people will have fewer opportunities to push your buttons or interrupt your (useful) patterns and you will have more choices about who and how you want to be in different situations.
Choice requires two things: intention and skill. The intention is an indication that you are prepared to make an effort to make something change. The skill is a tool you use to change something inside or outside yourself. You develop it through practice.
So how can you practice what you learn in NLP training?
1) On your own. Use reading, videos and imagination to create alternate ways of approaching and understanding the patterns you learned in class. Do mental rehearsal, notice the results, then become obsessive about changing just one thing at a time until you have found the most effective and elegant approach to a particular problem. Repeat with a new problem. Over and over again.
2) Practice with an accomplice. Play guessing games and ask for verification so you know when you are right. Play rapport games and get better at getting into sync and discovering how many different tools you have for making someone else comfortable with you. Play language games and notice what happens when you ask questions or tell stories. And you can even practice the change patterns and discover how to become even more effective at running them.
NLP is not the set of exercises you find in a course manual. NLP is the ability to recognize, replicate or interrupt patterns of thought and behaviour. You practice it by becoming more aware of the people around you, and more intentional about the impact you have. Every day. In every interaction.