I have more details.
**EVs:** They're Effort Values. When you battle specific Pokemon, you get a certain amount of effort values depending on the Pokemon. Then, every four Effort Values give you one more point in that stat when you level up. You can use Calcium, Iron etc to boost your Effort Values, and you can only have up to 510, so choose wisely! See [here] for more info.
**IVs:** Individual Values. As wolf_paw5 said, they come as soon as you obtain a Pokemon. They determine your hidden power type, Spinda's spots, Wurmple's evolution, and many more things. You can have up to 31 in each stat, IVs give you one stat point for each IV. Also, your characteristics are based off which IV is the highest. See [here] for more info.
**STAB:** It's **S** ame **T** ype **A** ttack **B** onus. As wolf_paw5 said, if you had a Pokemon a certain type, and that Pokemon used a move that was the same type, it would get a 1.5x boost in damage. Adaptibility, an ability boosts that to 2x. See [here] for more info.