讲课 is a separable verb (离合词) meaning 'to give a lecture' or 'to teach a class.' The verb 讲 and the noun 课 can be split: when you need to insert a duration, measure word, or object, the separation goes between them, e.g. 讲了一节课 ('gave one class period'). Unlike 教书 (to work as a teacher), 讲课 focuses on the act of delivering a lesson or lecture, often in an academic or training setting.