Well, it is very hard to say, if it will easy for difficult. It totally depends on the size of the school, number of international students and kinds of jobs that University gives for students. Yes, depending on the kind of job, it may involve interview. You may or may not get confirmation via email for job.
You can only work on-campus when you are studying, unless you are in PhD or doing bachelors, you cannot work for 4 years. Read this article on How to get on campus jobs in USA as International student