The main functions of the Security Council are to suggest mechanisms whereby disputes between states can be resolved and to enforce binding sanctions - economic or military - on states which are deemed worthy of them. Resolutions are theoretically binding and thus are often referred to as a type of "international law", but they are better understood as a political-diplomatic tool which can be wielded by the powerful. An insight into the horse-trading and bargaining that precedes any important resolution would disabuse anyone of the notion that "law" was an apt description for it, as should their unenforcability.
The idea behind the Security Council was to centralize decisions about war and peace in an institution where the world's biggest powers could resolve their differences through diplomacy and politics rather than on the battlefield. This is why the veto is so central to the Council - the institution was never intended to be democratic, but to reflect the will and consensus of the powerful. It was designed in an era before globalization when alliance blocs and spheres of influence were paramount. The role of the veto is to allow any of the great powers to block a decision which is offensive to them - rather than protecting their allies, clients or selves by war, they can do so with the veto. This model assumes, of course, that no war will take place without a resolution authorizing it, when in fact only two wars have ever been authorized.
Because the Security Council has become so blatantly a political forum, many countries who feel themselves as important as the current permanent members are clamouring for their inclusion as veto powers. They crave the legitimacy the Council can confer, even as its actual functioning belies its role as a tool of the powerful.