tl;dr: that's the duty of a professor to answer reasonable inquiries from students. As professors tend to be very busy, keep things simple and go straight to the points that you have a problem with.
If you visit Academia.SE, you will see that all academics are busy. Besides research and administrative duties, they are busy preparing classes, grading examinations and... answering questions during their office hours!
So, the first thing you should keep in mind is that, as a student, you have a right to ask questions and be given additional attention outside the classroom.
Before asking for some time with the professor, check the syllabus to see what are the office hours for that course. Most professors are required by their department to have official office hours where they are, roughly, "at the disposal of the students for questions". In case there is nothing, you can approach the professor that way:
Professor [Name], I feel I have some difficulties to understand the concepts of [topic] and [topic]. When are your office hours? I would like to visit you to ask a few questions.
Alternatively, some professors don't have a specific time in their schedule reserved for students' questions, and prefer taking appointments. This should probably be mentioned in the course syllabus, so check it, but otherwise, you can approach the professor at the beginning or the end of a class. Or you could send her an email. For example,
Dear Professor [Name], I am [your name], currently enrolled in your class of [topic]. I have some difficulties to understand the concepts of [topic] and [topic]. May I take an appointment with you to ask you a few questions?
In particular, when sending an email, it is a good idea to include the topics of the questions you want to ask, so that the professor can have an idea of the duration of the meeting.
I don't understand the difference between [concept 1] and [concept 2]. Could you explain me the nuance?
I read the solution of problem 2 in the assignment but I don't understand why you did [clever trick]. Could you explain to me how to get started on this kind of problems?
Very few professors would be upset by students showing interest in the course material. Most upsetting is the more frequent cases of students that don't understand the material and didn't care to do any extra effort to understand.
Of course, when approaching a busy professor, you have to be reasonable and "do your part of the job":
Try to identify the parts you don't understand as precisely as possible. "I don't understand anything" is not something a professor wants to hear. And is usually false, or show a complete lack of efforts.
Learn the fundamentals of the course material: definitions and statements of the main theorems (since it is a maths/programming class). There is nothing more annoying than a student asking how to solve a problem about a basic concept X when they don't even know the definition of X.
Note: this does not seem to apply in your case since it is a small class, but in larger classes, the usual course of action would be to ask your questions to the Teaching Assistant first, then go to speak to the professor if you still have unanswered questions.