Yes, you do.
You need an instrument to practice in between lessons.
In a lesson a teacher shows you a skill. Before the next lesson you practice this skill to make it stronger. This makes you ready to take the next step in your playing in the next lesson.
Practice is a huge part of learning an instrument, so you need your own instrument or access to one to do it.
So how do you get an instrument suitable for you, your child or teenager?
Ask your instrument teacher to advise you on the best instrument for you.
Teachers have a lot of experience teaching people of different ages and levels.
So, they are the perfect person to recommend an instrument that is a great fit for you or your child/teenager.
They also will have useful information about great places to get your instrument and supplies.
Then you will get a quality instrument that is fit for purpose and a good shopping experience.
Teachers are a treasure chest of useful skills and information.
Make things easier for yourself by asking their advice.