If the Key Signature has no Sharps & Flats, we are in the key of C (or A minor). We can do a circle of fifths in either direction (up or down) If we go down a fifth we have the Key of F - which has one flat, down another fifth to Bb (2 Flats), down again to Eb (3 Flats), then Ab (4 Flats) and
Db (5 Flats). If we go up a fifth we are in the Key of G (1 Sharp), up again to D (2 Sharps...