Welcome letter. What do non-U.S students need to know about making friends and keeping friends in college?
Sports if you enjoy them are one of the easiest ways to make friends. For example, usually there is a pick-up, spur of the moment game of soccer somewhere. If you love to play, cheer them on or join in. Check the boards of student unions for ideas of places to meet people. Student unions themselves are a good place to drink coffee, study or pretend to study, and check out groups of people you may enjoy. Look around your classes especially if you have any smaller ones, and look for people you have in more than one class. Find out if there is a study group for a class you like and join even if it isn't so difficult for you. Find writing groups if you can as that is one area non-U.S. students have trouble and you can help each other. In other words, look at what you like and enjoy, what you need to help you be successful at school, and look for other students who want the same thing.
Make an effort to meet people in the kind of places you enjoy spending time in. Don't go to a bar or a club to meet people if you don't enjoy spending time in bars or clubs. You'll need to join some groups that are "interest" focused, such as college level professional organizations in areas that you have interest/expertise in. That way you will be automatically meeting people that you have something in common with.
I am assuming you are taking about students who come to the US from another country. A student who comes from another country and returns after college may normally have some trouble keeping friends, but it is not impossible. In the modern age it is cheaper to travel by plane, and if the student comes from a neat place friends might want to visit. It is also easier than ever to keep in touch with social media like Facebook. I keep in touch with many distant friends this way. It is not quite as good as face to face, but it helps you feel a part of their lives.