Order of Sharps and Flats = BEADGCF
Order of Sharps = FCGDAEB
Notice how the two are a palindrome (forwards and backwards)
Circle of Fifths
All this tells you is which notes get sharp and flat in a song. Just remember the first 3 keys on each side.
A bar measure "resets" the notes from being replayed in the next measure - unless the accidental is in the key signature
Accidentals = a sharp or a flat
We say "D sharp" but we write "sharp D"
If I give a note an accidental the is not in the key signature, then the next measure does not play that note.