Don't feel embarrassed about your spoken English. People understand you are learning to express yourself in a new language and with practice you'll be fluent. In general, Americans prize independence and individual effort. In the academic world, they value independent thought. The most serious offense in the academic world is that of representing another person's work as one's own.
Plagiarism can result in disciplinary action.
It means getting help that a student is not supposed to get on an assignment, quiz or examination. Students are expected to do their own academic work without getting extensive assistance from other people. This does not mean that you cannot ask other students to help with class work. It is permissible to seek help in understanding what is happening in class and what a specific assignment is about. It is not considered proper to have someone else do an assignment for you or to copy answers or formation in a way that makes it appear that the answers were devised by yourself.