[مستر مصطفى عباس]

a teacher goes to school.School is a problematic word with articles because we sometimes mean the building, and sometimes we mean the institute or workplace.

For teachers, students, and pupils, we most often say that they go to school (no article) because we are talking about the institute or workplace. (We say someone goes to work, not goes to the work.)

Occasionally we use the article when we are talking about the building, most often when it is being used for something other than classes. For example, a town might hold a celebration in a school building, or Girl Scouts or Boy Scouts might use a school building for their meetings. Then we most often say the school. Note that I say “most often” because you will hear some native speakers not use the article here.

We’re performing a play at the school at 8 p.m. on Friday and Saturday.
Parents can meet with their children’s teachers at the school from 5 to 8 p.m. this Thursday.

In American English, school can mean anything from pre-K to post-doctoral studies, so a teacher can say I’m going to school two nights a week to do my master’s degree. The teacher actually means university classes for post-graduate studies. The article is not used because it is referring to the institute, not the buildingg