GTA, as many of you may know from the game's box art, stands for Grand Theft Auto. Grand Theft is the act of stealing items of a considerably high value, though the exact amount varies from jurisdiction to jurisdiction.
Way back when the first GTA game was released, stealing cars, as the title may suggest, comprised a considerably significant portion of the game. However, while it obviously still is a part of the series, GTA has expanded greatly, incorporating much more into its gameplay and story, while at the same time moving away from simple carjacking.

For those of you who are nostalgic about the GTA of yonder and wish that the most recent installment returned to the roots of the series, at least for a few missions, then this (albeit simple) mod is just right for you.
Car steal missions, as the name implies, has you steal cars. That's it, pretty much, no over complication. Modder 5mith has really captured the simple yet fun "get car x and take it to drop off point y" type gameplay that is found in several missions of the first two GTA games, and that appear, albeit in lesser numbers, in the more recent installments.