I applied online at join fashion inditex, and got a call a couple of weeks later, saying there's a group interview the following week in Regent Street London. In terms of this, make sure you research things about the company before hand, such as a new product comes out every two weeks, they have deliveries of stock twice a week, it's an eco friendly company, and all 8 brands in Inditex.
In the group interview, we initially filled out this form just with all personal details and preferred stores etc. Then a group of about 20 went into a room, we watched two videos on inditex and just were asked general questions (to the whole group). I answered a few times, but i'm not sure what impact this had as they don't know who you are, and didn't look like they even recorded who answered. Then after that, 3 different people from Inditex sat at the front, and there was like a 'speed dating' interview, where 3 people went up at a time to the front and are interviewed. It's not really as daunting as it sounds as no-one really pays attention and you can't really hear the interviews.
I got a call back a few days later saying that i'd been successful and then had a second interview at the store they assigned me to. That interview was obviously more in depth, with a lot more general interview questions. Then after that I got a call later that day, saying that I had been successful and that I had to sign my contract and go to an induction today in London. Overall the process includes a lot of stages, and it's obvious Zara do care very much that they have the right people working for them, but if you prepare and are confident, i'm sure you'll be fine.