Chain mail, though noisey, is a light and relatively effective piece of armour. It will stop most slashing attacks-
axes,
swords- but is poor against
bludgeoning attacks; A
hammer will hurt only a little less. It's also useless against thin
stabbing weapons, such as
pikes and
arrows.
It's normally worn over the top of some heavy cloth, to insulate- all those holes are bad for heat- to prevent chafing, and to give extra protection against stabbing weapons and cushion impact.
Sometimes, a cap, known as a Coif was also worn. Chain mail is one of the most common armours worn by infantry, as it was relitavely cheap and light. It was used on archers and other units that needed flexibility and to be unencumbered. Another common use was on pole-arm wielders.
The thing about chain mail is the word "Mail" means mesh, or chain; So you're literally calling it "chain- chain".