Submit a GRE score, letters of recommendation, CV, transcripts. These are reviewed by the graduate student admissions comittee. Successful candidates are invited to on site interview where they meet with faculty members to discuss potential projects

I did not have an interview. After obtaining admission to the PhD program, I send my CV to a professor and was recruited to this position. This kind of jobs are based on availability of funding and the fit between your research interests and your recruiter.