I am playing the oboe for Copland's hoedown. I usually play the clarinet but I picked the oboe fast. Anyways, how do you go from a low F and A to a low D really really fast without squeaking? For those who know what I am talking about it is the oboe solo at the beginning.

Noooo never used forked f unless you really really have to. It's regular f, then left f if you need to.. and only forked f if you're moving really fast from an Db, Eb, and F or something. But never use forked f if you don't need too!

Besides, you don't need to use forked f to get from an f to an a. Your problem isn't fingerings. It's something that an oboist might have trouble with from time to time- changing octaves. My teacher has told me that G is the highest "low" note. Play your low d and see how you're embouchure feels. Now play your A. When you're playing the a, think ahead of what you're embouchure should be like when you change to the d. Or try to play a with the low d embouchure.