Your confusion on this matter is understandable, but despite your misgivings, it might surprise you to learn that --unlike a divinely-sanctioned emperor-- there are no special protocols required when communicating with a professor, especially in relation to a standard academic matter. All that is required is basic courtesy and clarity, as would be standard in any professional communication.
Whether you are communicating by email or directly in person, it is important to remember that there are no special magic words that you need to say when dealing with basic academic matters with a professor. Be as clear and polite as you can, and get to the point about what you want. Basic courtesy with pleases and thank-yous will be sufficient to ensure your communication goes well, and being clear and succinct will help your professor to deal with your matter without having to waste a lot of time. Many administrative matters (e.g., reviewing a mark, applying for a program, etc.) involve the application of university policies, and it will be helpful if you have already read the relevant policies prior to communicating with your professor.
Emails: Many of these matters can be dealt with by email. Composing an email to a professor is no different to composing any email in a professional context. You should be clear and courteous, and get to the point of what you want to ask them. Ideally you should use a level of formality that would not be out-of-place in an office context. It is good practice to use the person's academic title (Prof, Assoc Prof, Dr, etc.) and spell their name correctly; this is easy to do, since academics almost always have a university web-page with this information, and a quick web-search will find their information. If you are not familiar with how to write an email in a professional context, there are many, many, many, many websites that give tips on how to do this. Some general tips are:
- Write your email in a professional manner;
- Have a clear subject line that tells them the topic;
- Remind them who you are (unless they know you well);
- State your request clearly, and give relevant context;
- Make your request consistent with administrative procedures at your university; and
- Ask your professor if he/she requires any further information.
Professors are generally quite informal in their email communications (with some exceptions), and they are also used to dealing with young students who have not been in a professional environment before. This means that the bar for communication is low; if you fall short of the ideal standard of professional communication, your professor is not going to be angry at you. Just try to be clear and polite, and you will be fine. It is good practice to get into the habit of professional writing while at university, and these situations offer you a good opportunity to practice your communication skills. If you would like special help with this, go to the academic-skills center at your university and ask them to teach you how to write a professional email.
Direct meetings: Emails are generally the best method of communication when dealing with simple administrative matters. This is because they give both parties a record of communication and they allow the academic to deal with the matter at leisure. Nevertheless, for some academic inquiries where a back-and-forth is required, it might be quicker and easier to talk directly to your professor in-person. Depending on how important the professor is, it might not be easy to get much time with them. You might require an appointment, or it might be possible to just knock on their door and ask to speak to them, or see them after class. (If you are in a course with this professor, they probably have set consulting hours for the course when you can come and see them.)
Dealing with academic matters in a direct meeting is similar to email. Be clear and polite, and get to the point about what you want. Remember that you are talking to a busy person with lots of things to do, so you want to help them to understand what you want and deal with the matter quickly. There are generally no special formalities required, but it is good practice to communicate in a professional tone.