教课 is a separable verb (离合词) meaning 'to teach a class' or 'to give a lesson'. The object 课 can separate from 教 when adding duration, measure words, or other modifiers: 教了两个小时的课 ('taught two hours of class'), 教过三次课 ('taught the lesson three times'). You cannot put a direct object after 教课; instead say 教学生课 or 给学生教课.