We used the Walk-Up Wait List at Cafe Orleans in mid-August and for River Belle Terrace this past Saturday. Like others have said, you use the Disney App to do this. You have to wait until the restaurant you want opens (both restaurants we went to open at 11:30) and then you can check wait list times. We were able to get return times of 45 minutes both times, with our tables actually being ready 35 minutes and 30 minutes after joining the wait list.
Just a warning, Olgas Cantina's wait list gets full first thing in the morning for the entire day so if that is somewhere you are interested in going to, you will want to get on that wait list first thing in the morning. I assume they open early because the wait list was full by 9am both days. Nothing their interest me or my wife so we have never tried to join that wait list.