For any major played, (g major, d major, etc.) do we play everything else as a low/natural? (Ex. G major only uses every f as a f sharp. so would c and g be played both as low/natural in the piece if they are there?)
I THINK I understand your question!
Yes, when playing a scale the key signature tells you which notes are to be played as sharps (or flats). The remaining notes are played natural.