The Ork answer to Assault Marines, Stormboyz are greenskins with even less instinct for self-preservation. These young greenskins voluntarily strap themselves into highly unstable and barely functioning missiles that we like to pretend are Jump packs.
Stormboyz are straight up odd. When the orky lifestyle means you can do whatever you want whenever you want, not every young and bold ork actually does so; they're either overwhelmed by the possibilities, or simply too ornery from being a teenager and therefore decide that they want to be edgy. Either way, a young Ork who has reached a few years of age may join the Stormboyz. The Stormboyz have their own sort of culture that's quite unlike most other greenskins. They march and drill, they respect authority and do what they're told, they keep their equipment and uniforms clean... hell, they have uniforms. Stormboys don't just practice fighting by getting into a scrap like other orks, they actually train, and in battle this training seems to work. Stormboys are known for cunning plans and suspiciously well orchestrated (ork-estrated?) strikes. The 4th Ed Ork Codex entry on Stormboyz is renowned for being the most hilarious Codex entry in a book full of hilarious Codex entries.
In 8th Edition Stormboyz are fast, possessing a standard move of 12". Due to their Jump Pack and Fly keywords they can cross any obstacle, and when they Advance they can even choose to move a full 6" rather than rolling the dice. However, if they do so, you must roll a D6 for each model in the mob, and if you roll a 1, a boy dies from a mortal wound. He's either blown up in midair, faceplanted into the ground, hit a tree... use your imagination. Even so, this ability to move up to 18" before any buffs are even taken into account makes Stormboyz great for capping objectives, tying up critical enemy squads, and eliminating back-field support units.
In terms of their statblock, Stormboyz are absolutely the same as typical Slugga boys at a slightly higher cost (9 points each). Given the benefits these silly rokkit packs offer, that's pretty much a steal, just keep in mind that they will die fast if focused before they can get stuck in. Like standard boyz mobs, the Stormboyz can bring a single Nob who comes equipped with a slugga and a choppa, and can take additional weapons from the Nob Weapons list. Unfortunately, other than the options available to the Nob the Stormboyz themselves are rather lightly equipped, carrying only a Slugga, Choppa, stikkbombz, and a standard-issue Ork t-shirt for armor. However, Stormboyz do have an advantage in that unlike Kommandos, a unit to which they are often compared, they can have a mob size of up to 30.
The Stormboyz' most important ability, and the real reason why you would take them, is because they can perform a Stormboyz Strike. Essentially, this is a Deep Strike that allows you to place the mob anywhere on the table that is not within 9" of the enemy at the end of any of your movement phases. There is nothing quite like thirty hooligans appearing within 9" of the most vulnerable part of your opponent's army, ready to sink some sharp bits into some heads.
There's also a popular git immortalized on Suptg's archive, going by Uzgob Rokkit-Ranga, who WAAAGH'd where no Ork had WAAAGH'd before, nor since.