Many items found, especially early in the game, will be unidentified or partially identified. Weapons and armour can be identified by being worn and used in combat, and can be removed if found to be of poor quality. Some characters learn to cast spells to identify the runes on wearable items that define their properties.
Staves, rods and wands can often be identified by being used against monsters, but be aware that some of these magical items can have negative effects. Only use this approach when facing easily defeated monsters. Consuming unidentified potions and mushrooms can be risky, so the risk-averse player may prefer to sell them in the town. Ammunition can normally be identified by being thrown or fired at a monster, and typically the worst thing that can happen is that the attack does little damage to the monster. As with staves, wands and rods, do this when facing a monster than can be easily defeated.
Scrolls can normally be identified by being read, but some scrolls have negative effects. Your character may have a very short life if they read a scroll that summons a horde of undead monsters. If using this approach, it’s a good idea to position your character on top of some stairs so you can quickly escape if a mysterious scroll leaves your character surrounded by monsters.
With weapons and armour, your character will in time learn their inscribed runes.