Gold and Silver days are not 'extra days off however are a way of fixing your days off from 3 months for Silver up to 12 months for Gold days. They can be booked in pairs (or blocks of 3 on the 787). I generally use them for birthdays or maybe a bank holiday weekend. They can also be tagged on to leave days meaning 7 days of leave can be bumped up to 11 days off using a couple of golds and the automatic free days off we get around leave.
All leave and Golds/silvers are done online. There are various leave bids from the A bid (most points) down to the open bid. The A, B and C bid is done by expressing preferences and the leave desk closed for a couple of days each time to grant bids depending on a points based system. Those with the highest points are those who have had christmas or popular holidays off in the past and obviously the lowest points are those who don't care much about August/July/Xmas etc etc.
Then the bid is open on the C bid and what's left is cheap as chips point wise and if you are happy with weeks off outside of school holidays then there's usually plenty left so you can go online and get your leave. It's a live system so if it's there, it's confirmed instantly.
Hope that helps.