To give some more detail, but not enough to confuse you, RNG refers to the process of predicting the game's pseudo-
random
number
generator. This is done with all sorts of calculations using all sorts of processes, but when done properly, it's possible to basically control when you get shinies and good IVs. It's possible to do this on Emerald, the 4th Gen games, and Black and White. If you're at all interested, I recommend starting with Standard abuse in BW. By far, it's one of the easiest ways ever (though, you do need a DS/DS Lite). Also, you can't RNG for shinies in BW without an AR or similar device, and that kind of ruins the whole point of RNG abuse (to get what you want without hacking). And sadly, using RNG in BW for breeding is pretty hard to do at this point.
PKMNTrainerBrandon said:
So I would have to keep catching Dratinis and/or Dittos and see if they have the appropriate IVs for attack and speed?
Yes. There's nothing else to say. Though, you don't need an IV calculator for your purposes. Just take whatever you want to check to the IV checking man (in BW, he's right by the entrance of Gear Station [after you enter, not outside]). He will tell you what it's "overall potential" is, and what he believes is it's best stat. If he says Speed, you're halfway there. Then, if says it can't be better, you have a 31 Speed IV. Repeat for Attack.
And if you truly want to easiest way to get a Dratini with what you need without having to use RNG, have someone else do it for you and trade the result.