The word "Einschulung" refers to a child's first school day. In some federal states, children celebrate this day in a small festival that might even take place on a Saturday rather than an actual school day. In other federal states, the first school day is celebrated as a special event but on a regular school day. The specific date first-graders start school differs from state to state - it often is a few days before or after the first day of each new school year which (in all federal states) begins after the summer holidays. You can find the exact dates at schulferien.org.
Every school independently plans the start of school for first-graders. Therefore, the procedures often differ from school to school. It usually includes a welcome speech from the school administration and your child's teacher. In some schools, there are also joint services. You can inquire from the school management whether your child is required to attend. Such a service is often a voluntary offer to the students and their parents. After the service, children go to their new classroom to meet their classmates and teacher. Then, the teacher talks to the children about their first days at school and shows them the school building. Schools usually strive to make the first school day fun and memorable for children.