Holiday is four 'block' weeks, and a number of floating days- seems like hundreds!
Block leave is one week spring, two summer and one winter, and will be noted in the 'base roster'.
Whatever you're allocated now, the base will move on a set number of weeks each year, so you won't always be stuck with two weeks in may when you want two weeks in august.
Blocks can be moved around in each period, subject to availability or by mutual swap with a colleague. This movement doesn't affect the base for next year.
Depots have strict local rules, agreed with the Union, on how to apply for swaps and when the base becomes final and no more changes are permitted. Speak to the Union about your committed Sundays, you'll not have one during your two week block, but can either before or after the single weeks, which can be tricky for flying or recovering.
Floating days can be booked ad hoc, subject to availability. If booking weeks for a holiday like this, you may find that you'll get Monday, Tuesday, Thursday and Friday off, for example, but Wednesday is full so you'll be working that day, which is a pain if you plan to be in Rome. You can look at the shift roster and see if someone will exchange shifts with you, but that's not always possible.
Floating days can't be carried over and won't be paid out, so use 'em or lose 'em.
If you are planning a special holiday eg anniversary or once in a lifetime- like Disney- then speak to your Union rep and they'll tell you how to apply directly for specific blocks, but this has to be done well in advance
With canny use of floating days and your regular rest pattern, you can get a long break with the use of a few extra days.
Importantly, be on top of when the base is released and when it gets finalised. Be on good terms with all your colleagues, as you might need to swap a block/shift with them.