Classrooms in the United States are typically learner-centered. Rather than listening to lectures from a professor and memorizing the content, it is more common for students to listen to lectures that are interspersed with class discussion and activities. Students often direct their own learning and engage with a wide range of ideas and perspectives held by their classmates.
Students are expected to actively participate in class. For example, asking questions, sharing their opinions, and adding information to discussions, when appropriate. On the other hand, students can politely listen to other classmates, letting others have a chance to speak. If an instructor asks a student a question, it is good for them to answer the question, even if the answer is wrong. It is also fine for students to say that they do not know the answer to a question.
There can be a level of informality in the classroom. For example, students tend to dress casually when they go to class and do not stand up when their instructor enters the room. Also, most instructors allow students to chew gum and eat during class. Smoking is not allowed in class, however, and it is not appropriate to talk on the phone during class.
Inclusivity and interaction are valued inside and outside the classrooms. In the United States, it is a developing norm that individuals will identify their personal pronouns (such as: she/her; he/him; they/them; ze/hir) when they first introduce themselves in classes to their instructors and classmates. For more information on pronouns, MyPronouns.org (https://www.mypronouns.org) is a good resource.
It is useful for international students to get to know their classmates and develop relationships with the other motivated, serious students in their classes to study with or check in with on homework assignments. Asking other classmates for their contact information (email / phone) for these reasons is considered normal.