American professors are, in general, open to interactions with students. Most professors will post office hours. You can also make an appointment with a professor outside of office hours.
If you are going to meet with a professor, be prepared for the meeting. Have questions you want to ask prepared in advance. Be respectful by showing up on time. You don’t want to miss an appointment, but if you do let the professor know ahead of time.
One thing that American professors hate is when a student tries to negotiate a grade. Excuses like: “I am going to lose my grant from my country if I don’t get a higher grade in this class” will just make your case worst. American faculty is generally very resistant to any attempt by a student to have a grade changed.
If you communicate with a professor in writing via email, make sure to give all of the background needed. You need to first explain your situation, and then ask for help.
When you speak with a professor, slow down what you say. Most faculty are comfortable with a number of international accents, but may have trouble understanding you if you speak too fast or too softly.
Generally it’s better to meet with your professor by yourself. Some international students like to travel in groups with others from their country. It can be overwhelming when several students show up in a professor’s office. There’s generally no need for this. If you think you won’t be understood or won’t be able to understand what your professor is saying, then a classmate going with you would be ok.
Finally, American faculty don’t feel comfortable when you present them gifts or offer them something of value. Gifts are not expected and should be discouraged. Never give any hint that you will offer something for a grade..