How do Holidays in Jobs with 4 Day Weeks Work?

I've applied for a job with a 4 day week set up and its a 37.5 hour week, no condensed or extended hours or work - just a free day all but gaurenteed every week of the year, set up.

I don't want to ask questions about perks at the interview, I'd rather ask questions that might help me with the job, and there's no detail on the advert about holiday entitlement and so on.

I am wondering how holidays work? If I wanted a week off would I only need to book four days off work? That seems to good to be true as beyond getting near 52 extra days off a year I would also get another week or so annual leave a year.

Anyone else have a job like this, and how does it work?