Oi, ya git! Get in, wese gonna have some fun!
Trukks are the very basic vehicles used by da Orks in Warhammer 40,000. While GW emphasizes that it's a specific vehicle, in reality it can be any Ork vehicle smaller than a battlewagon. It is by far the most common Ork vehicle, used by every force from the most basic Boy to Warbosses and Goffz to Evil Sunz. Most commonly they're the barebones chassis of some looted vehicle, an engine, and whatever scraps of metal or weapons are bolted onto it. Usually they're owned by a Nob and used to carry a mob of Boyz to the front.
If a Mek (or any Ork or neckbeard in general) gets their grubby mits on the burned-out shell of a Rhino, Ghost Ark, or any kind of small transport, it will most likely be kitbashed into a trukk of some variety. Given the Ork fluff, simple rules in terms of crunch, and the lenient "counts as" rules at most tournaments when it comes to Ork vehicles, the trukk has the most variety and customization potential out of any vehicle (and maybe any model) in the entire game.
The Trukk can be taken as a Dedicated Transport for most Ork infantry units. For a 12 man Open-Topped transport with T6, 10 wounds, and a 4+ save, it is
a steal at 30 points pretty reasonably priced at 59 points, as of 8th edition. The vehicle comes with a single Big Shoota by default, but you can also slap a Wreckin' Ball and/or a Grabbin' Klaw for some extra melee crumpin', or take a Stikkbomb chukka to give it a little bit more ranged firepower at 12" or less. Of course, since it is Open-Topped the Orks riding inside can all shoot out as well. Sadly, Trukks lost their boarding planks somewhere along the way to 8th edition.
Trukks come with the hilarious rule Ramshackle, which means that any time it takes a hit with a damage characteristic of more than 1, on D6 roll of a 6 that damage is reduced to 1 point. Laugh your ass off as your opponent's Lascannon takes off nothing more than a piece of sheet metal.
Overall Trukks have limited ranged firepower that is mitigated by their Open-Topped ability, and they can be upgraded to be mildly useful in close combat. Try not to go crazy with upgrades you won't need, though, as Trukks are meant to be cheap, expendable transports for your Boyz and nothing more.