Attacking is simple in Angband. If you move into a creature, you attack it. You can attack from a distance by firing a missile or by magical means (such as aiming a wand). Creatures attack in the same way. If they move into you, they attack you. Some creatures can also cast spells from a distance, and others can use various breath weapons (such as fire) on you from a distance.
Creatures in walls can not be attacked by wands or other magic attacks normally stopped by walls, nor can they be shot at with bows and arrows. Tunnelling into the wall (using the “tunnel” or “alter” command) will allow you to attack any creature in the wall with your main weapon. This applies to creatures which “pass through” walls: if they “bore through” walls, the wall is no longer there, and the creature can be targeted normally.
If you are wielding a weapon, the damage for the weapon is used when you hit a creature. Otherwise you get a single punch which does minimal damage.
You may wield one weapon for melee combat, and also one missile launcher (bow, crossbow or sling). You may also wear one amulet (around the one and only neck of the character), two rings (on the two “ring” fingers, i.e. the third finger of each hand: a magic ring does not function when worn on any other finger, nor may two be worn on the same finger), one light source, and a full set of armor – body armor, shield, helmet, gloves, boots and a cloak. Any or all of these items may provide powers to the character in terms of bonuses to-hit, to-damage, to-armor class, or to other stats.
Firing a missile (while wielding the appropriate launcher) is the only way to get the “full” power out of the missile. You may of course throw an arrow at a monster without shooting it, but you will find the effects will not be what you had hoped.
Hits and misses are determined by ability to hit versus armor class. A hit is a strike that does some damage; a miss may in fact reach a target, but fails to do any damage. Higher armor classes make it harder to do damage, and so lead to more misses. Characters with higher armor classes also receive a damage reduction. This is not true for monsters, whose AC only affects the character’s difficulty to hit them.
If you wish to see how much damage your weapon will do, you can Inspect it. You will find the number of blows and how much damage you would do per round, including information on whether your weapon damages other types of monsters differently.