There are generally two overall stages to the interview process. A general interview and a styling task.
The general interview will go over things like your availability, past experience, and why you want to work for the company. It is a good chance to show off any knowledge and passion you have about the brand and why you want to work for them specifically, Give any interpersonal, retail, or customer related experience. This part of the interview is pretty generic, just answer the questions the best you can.
It would be a good idea to prepare a few things in advance e.g. an example of a time you showed initiative and the result, your strengths, etc.
For the styling task they just want to see if you know what goes together well and may ask you something along the lines of - select 5 items which would go together well for a weekend break - as a sort of capsule wardrobe. This may be a specific scenario e.g. for a certain type of customer. Have an understanding of the company's general clientele and what they might wear/ what is trending.
Really, the most essential part of this task is that you can give adequate reasons for why you selected what you selected.
The current system - you will be scored on a number of elements, likely be along the lines of: experience, how personable you are/ your communication (for customer service reasons), the styling task, and availability.