Don't dwell on the reasons for your absence. The first few minutes of class are often used for vital announcements, such as upcoming tests, due dates for assignments, etc. Better late than never is usually a good rule of thumb, but not always. Note the professor's reaction when other students are late, then guide your own actions accordingly. If the reaction to student tardiness is somewhat more stormy, it may be better to miss class than to call attention to yourself in an unfavorable light.
Professors usually announce office hours at the first class meeting each semester.
It is to your advantage to know your professors and for them to know you. Make an appointment to see each of your professors no later that the fifth class meeting. Appointments may be made before or after class or over the telephone. Remember, teaching is not your professor's only responsibility. The purpose of meeting with a professor, regardless of your level of interest in the course, is to enhance your understanding of what is going on in class.