
On the Kennel club Website http://www.the-kennel-club.org.uk/ click on the left on Information Guides and read the one on stud dogs.
Be awre that you will need to ahve yoru dog Hip Scored (£150 rough cost) then find a specialist cardiologist (join one of teh Boxer clubs and you will get the details from them) to have him heart tested. There is a high incidence in the breed of heart problems,a dn he would have to be graded as 0 or 1 to be bred from responsibly.
After this you need to realise that it is the owners of bitches that dhoose the dog to best suit their bitch, so you will need to show him to prospective bitch owners and he will have to compare favourably with his rivals. This basically means you weill need to show him.
Any bitch owner that would want to use yoru dog just because he was available is not the sort of person you should acept as they are unlikley to hae the welfare of the breed, their bitch and any resulting puppies as their priority.
Also as Boxers tend to be male dominant/intolernat you will find that if he isn't already then being used at stud will likely make him so or make him worse around other male dogs.