A key signature is normally found directly after the clef symbol, it determines the set notes that are to be played higher or lower than the corresponding natural notes. this will stay the same until the end of the piece unless there is a key change. the image below shows the time signature at the start of a piece of music.
to work out the key signature of a song we need to know how many Sharpe’s or flats are in a given scale. to do this we can either work out each scale to find it out or we can use the circle of fifths. the image below shows the circle of fifths with this it shows us how many Sharpe’s or flats are in a key and what they are so it can be wrote down.
for example if we wanted to know what notes are in the key of D thenw e can look for the note D and see that there is a G and a D in the key and scale.