There is a preliminary interview with standard HR type questions to determine if you should be invited to shell day.
You are invited to a dinner before the Shell day, where you are taught about the interview process and go to dinner with some current employees.
At Shell day, you do a variety of business cases, both alone, in small groups and one large case with a big group. The last case is solved as a group with all of the interviewers in the room assessing how you interact with each other.