You will be issued two pairs of boots. They are often uncomfortable, but get better. IF you have very bad feet you may get a biff chit for a slightly different pair to fit your clown feet.
When you finish you can go out and buy proper boots (I have 2 pairs of Altbergs which are the business, but my issued I use for normal work).
In the meantime, if you have an overwhelming desire to spend money go out and buy a couple of good supportive insoles; those made by 'SOLE' are excellent and you get 30% discount for forces. You may need to go up 1/2 a size to fit some insoles, but it is well worth the money, and can save your knees.