It consists of a narrow metal spike set at right angles to a haft and is generally used one-handed. Shorter spiked versions tend to blur into warhammers.
The sole point (ahem) of this weapon is to penetrate armour - the weight of the head, combined with leverage supplied by the haft are concentrated into a narrow area by the tip of the spike giving them an excellent chance of punching through most forms of protection if a clean hit can be obtained.
Like most piercing weapons the pick sacrifices raw damage dealing capability for penetration and has an above average chance of getting stuck in the target. Many users may consider it over-specialised for general use but against a heavily armoured opponent it may be a life saver.