After you apply online, if a recruiter likes what they see in your application, they will contact you and conduct a phone interview. During the phone interview they will discuss the position duties, pay, and hours. They will also ask a few questions similar to the types of questions you would get during a real interview ("tell me about a time when..." ,etc).
After the phone interview, if you express interest in the position, you are called in for a group/panel interview, during which you perform a few team exercises, such as interviewing another person, and creating an advertisement. I think this gives the recruiters a chance to evaluate your personality and how you react to different situations.
If you pass the group interview, you are then called in for a one on one interview with both one of the recruiting heads, and the team lead in your department. The questions for this interview consist of a lot of customer service scenarios (what would you do if this happened?) and a lot of "tell me about a time when..." questions. Not extremely difficult, but not the easiest interview I've ever had either. Both the group interview and the one on one interview each took about 1 hour. I mostly enjoyed the group interview and the chance to meet some interesting people.
After the 2nd interview, I didn't get offered the position, but I think it may have more to do with my background and qualifications rather than how I did during the interview. If you know you are qualified and have a background relating to the grocery industry, or are just starting out (need a job while in school, etc). go for it!