Can someone help me create a character? I must describe him/her physically and mentally, what he/she looks like, how he/she thinks, dresses, behaves, and so on.
You are the person who needs to make the decisions concerning your character. Perhaps some suggestions can help you with that process.
First of all, it might be helpful to make some choices about this person you're going to create. Do you want to invent a male or female? Do you want this person to be a child, a young adult, an old person? Is this person going to be similar to you or very different? Are you going to be required to use this character in developing a plot of some sort in the future? If so, that could have a major impact on the person you create - make him or her someone you will be able to use in your future writing project(s)!
This assignment sounds like your opportunity to dream. If you want to create a great-looking guy with long, wavy blonde hair, vivid blue eyes, a well-muscled and tanned body - this is your chance! Once you decide where he lives, you can give him a job and/or hobbies that fit his environment. Environment and surroundings will influence the way your character dresses and may shape his/her attitudes and thought patterns.
The attached link may give you other viewpoints from which to think about your character as you are developing him/her. Use lots of adjectives to be descriptive and have fun with the assignment!