Office hours are a great thing in theory. The idea is that each teacher has a set number of hours (about three per week) during which time they are available for students to stop by and ask questions or seek extra help or talk about a homework assignment. These hours stay the same so students know at any given time when they can visit the teacher. It serves as an additional resource on the off chance that you perhaps did not have enough time during the lecture to get your question answered.
Free tutorials are a great way to really comprehend those difficult physics concepts. Free tutorials on educational websites can go above and beyond office hours and the concepts you are presented with in class. If you are out sick or you just didn't quite hear something in class you can turn to a free tutorial online and fill in the areas that you are missing. You can review lessons you already learned to double check that you understood them. You can test some practice problems to make extra sure that you have a thorough grasp of the materials before you move on to the next section.