The Stinger is automatically acquired upon claiming the Djinn from the Foundry. Note that this weapon also takes up one Sentinel inventory slot.
Similar to the Acrid, Stinger's projectiles will deal guaranteed Toxin status effects no matter what elements or status chance are present on the weapon. The status chance listed in the Arsenal is the chance to proc the element the weapon is modded for.
Projectiles curve off target at range similar to other 'bolt' weapons (Boltor, Bolto, Akbolto and Acrid), though deviation possibly starts at a much closer distance for the Stinger.
Ammo Drum has no effect on the Stinger because it does not have a maximum ammunition.
Using multishot mods will send multiple darts which will all have independent travel trajectories, effectively giving this weapon a "spread" shot and increase the probability of hitting the enemy.
When facing Grineer, consider slotting in Electricity damage mods to create Corrosive damage. Corrosive damage is even more effective against their armor than the base Toxin damage, and can reduce their resistance to your normal attacks.