Each university in the Unites States of America sets its own admission standards so there isn't the same criteria for all the students and the university can decide which applicants meet those standards. The fee for each application is between $35 to $100.
After the selections of the universities you want to attend, the best of all would be to contact each university for an application form and more admission information for the international students. Moreover, for a graduate or postgraduate program it's necessary to verify the admission requirements. Some programs require that you send your application directly to their department.
Admissions decisions are based on students's academic record and different test scores, such as TOEFL, the SAT or ACT (for undergraduate programs) and GRE or GMAT (for graduate programs). Admission decision is based on your academic results and motivation.