bruce bailey said:
Usually any notes an octave higher or lower would not be affected. This is typical but not ALWAYS true. When in doubt, check the score.
This is an important observation because to the uninitiated it's not always clear and worse, from the person doing the notation, it's not always clear what they want.
If you are in the key of G and your first note in a measure is a first-space F with a natural sign in front of it, if you see any other Fs in that measure in other octaves they are F#s (from the key signature). Normally the extra accidental
only affects the note directly following the accidental and in that octave only. Conversely, if you are in C and you have a first-space F# ,the succeeding Fs in other octaves are F naturals (from the key signature).
(Many writers, like me, will notate in succeeding octaves whether or not that note remains changed or no, as a safeguard against ambiguity. Ie. in G, if the first F is notated F natural, I'm likely to put a (#) before a succeeding F in another octave.)
This probably will not apply to you for some time, but if the music is atonal, or with many shifting tonalities, you have to be careful. So like Bruce says and check the score.