From Exterminatus Manual
Tyranid Warrior (Warrior)
The Warrior is the closest thing to a "basic" large class in the ever-diverse and ever-mutating forces of the Hive Mind. It is capable of both long and short ranged combat with a variety of symbiotic weapon creatures.
Warriors are armed with a pair of Talons for close quaters fighting. Talons are the warriors secondary attack regardless of their symbiote weapon.
The default weapon symbite of warrior is the Devourer which can fire a rapid barrage of flesh eating maggot up to medium range. The devourer is less accurate and stores less shots than it's marine counterpart the boltgun, however it can regenerate ammunition indefinitely.
Warriors can choose to equip a Deathspitter for ranged fighting. The Deathspitter fires an acidic bug that splatters on impact to cover an area with corrosive acid. The deathspitter can store only a few of these bugs at once so it's limited to bursts of 3 shots.
For a few points more Warriors can equip a Barbed Strangler to gain an indirect ranged attack. The Barbed Strangler symbiote launches a Barbed Strangler creature, which latches on to the first thing it hits and lashes out with fast barbed tendris at the enemy. Each weapon symbite can only manage one projectile at a time.
Like other tyranid weapons the warrior's weapon symbiotes regenerate their own ammunition. In a sustained fire fight warriors have the advantage of never running out of ammo or needing to reload, however they are best used to sap the enemies heath before going in for the kill with talons. Warriors don't make the best marksman, so they need all those advantages.
Talons have a much greater reach and have a more powerful impact than the marine's standard knife, making the warrior far better at hand to hand combat. Because warriors dual wield their talons they can hit 2 targets with each attack making warriors more effective than marines against groups of enemies.
Learning the tactics specific to each of the invidivial weapon symbiotes will greatly improve your effectivemess as a warrior.
Warriors are also much larger than humans presenting a larger target, especially from the side. Beware of ambushes. Being big they cannot always access areas that humans can. Warriors are however the fast and cheap class, giving them an advantage in the race to capture objectives.