Wear

Wear, [w], is a command used to wear pieces of armor and shields. Items of armor that layer over the torso must be worn in an 'inner-to-outer' fashion: shirts, then body armor, then cloaks. Use the [T] command to take off worn armor. Wearing and removing armor takes some time; the number of turns depends on the type of item.

To wear accessories such as rings or amulets, use [P] to put on the item.

Strategy
You can determine the bonus of enchanted armor by wearing it to see the change in armor class. You can identify many magical items by wearing them, especially in conjunction with enlightenment.