You don't need to explain that you are introverted, but write more about what you are good at. In this case, you are recommending yourself to the employer. You don't need to say anything, just say something that is good for you. When writing about your specialties, don't write about your personal interests, such as singing and dancing. Try to write personal strengths that are helpful to your future work, such as communication skills, coordination skills, leadership skills, etc. This specialty can not only show that you are mature, but also be beneficial to your future development.

You can write like this:

I am a person who loves life and works hard. In my study and life in high school, I not only learned a wealth of knowledge, but also improved in all aspects. I never flinch in the face of difficulties. I always use my head and try my best to solve problems and overcome difficulties. And every time I solve a problem and overcome a difficulty, my confidence has been improved. I believe that as long as we have enough self-confidence and redouble our efforts, we will certainly overcome all kinds of difficulties and obstacles and lead to the other side of success.

In the university, the rich and colorful social life and orderly and tense learning atmosphere have given me different degrees of exercise and test in many aspects; Integrity and hard work are the principles of my life; Calmly calm is my attitude when something happens; My extensive hobbies have enriched my life; Many friends make me feel rich. My strong sense of professionalism and responsibility enables me to face any difficulties and challenges.

The above can be modified according to your actual situation.