The Practice Arrow is a type of arrow that does no damage at all. Despite having no damage, it can still be used as a lethal weapon, owing to additional damage potential given to it by the bow. The practice arrow looks exactly like the iron arrow.
The only use for the practice arrow is when practicing archery at Angi's Camp, and, as with every in-game item, can be acquired via console commands on PC. Angi only gives 10 practice arrows a time, and requests that the Dragonborn uses only practice arrows. 20 more arrows can, however, be found around the training camp. If Angi dies, it is impossible to obtain more arrows without the use of glitches or console commands.
Infinite arrow exploitation
An infinite amount can be obtained by dropping them and asking for more or giving one to a follower; so that they will fire an infinite source of arrows.
Use in combat
Practice arrows are especially useful in circumstances where the player wishes to keep their target alive. For example, a practice arrow may be used with a weak bow (such as a long bow) and a frenzy poison to increase the chance the poison will be delivered without killing the target. A paralysis poison can also be used on them as a way for the player to safely get close to the target to cast Soul Trap. Additionally, standing while firing will avoid receiving a sneak damage bonus.