After applying online, I was called in for an interview. The Manager interviewing me asked me several basic questions involving what I'd do or had done in several problematic situations. These are common-sense questions about situations likely occurring to anyone who has attended high school or had a job before.
If you do not like the question or don't believe you have the ability to have a good answer for it, you can ask for an alternative question. I'd advise asking for the alternative question if possible, but that's not a complete deal-breaker as far as getting a job at Walmart is concerned. The Manager interviewing you is looking for a thoughtful, common-sense, well-spoken, and sincere answer to the question being offered. There is really no "right" or "wrong" answer to the question. Rather, you should ask yourself if your answer demonstrates you gave thought to the situation you described and tried your best to deal with it in a sensible way.
If you are called to an interview, there is a very good chance you can get the job depending on two things. The first is "availability." Walmart is a retail company and expects its employees to be on-the-job during the hours that most people prefer to shop, which includes weekends. While some Walmarts may be flexible, the Walmart I worked for expected employees to be available any time, and schedules could change drastically from week to week. If you can do this, that's a big plus. Second, your answers to the interview questions ought to come with little hesitation and provide good, simple answers that show you can deal with problems in a practical manner.
Walmart will ask for at least a background check and in the cases of some Management positions, a drug screen. The results of this will take one to seven days. If you've moved a lot, the background check can take a little extra time.
How should you dress? At least in my experience, candidates who dress neatly and avoid overly-casual apparel give a better first impression. It's not necessary to wear a suit/tie or dress unless that is what you are most comfortable in, although it never hurts. The daily dress code involves at least a collared shirt and slacks (not jeans), so rising to that level is a must. There's no need to invest in an expensive outfit.
Other hints: Put away the phone and have it on silent the entire time. Be on time for the interview. Be sure all of your contact information is correct so that the HR team can get back to you (and hire you!) as soon as possible.