#1
When playing a song with a sharp or flat in front of a note do you play it like that throughout the whole song, only for that measure, or until theres a natural to tell u to play it normal?
#2
In a key signature you play a flat instead everytime. Unless there is a natural sign in front of it which cancels it out. But if there is a flat in a measure then it's just till the measure ends unless obviously you hit a natural before that... I hope it helps
#3
Revenga47 is right - if a note is sharpened or flattened, it's ONLY during that measure, unless canceled by a natural. If it's a key signature as indicated at the beginning of the piece (ex. one sharp is G, two sharps is D, one flat is F, etc) then all necessary notes are sharpened/flattened throughout the entire piece, unless a natural cancels it accidental for that measure.

MadTaco
"He who controls the past, controls the future. He who controls the present, controls the past." - Orwell