Starting with any note if you ascend by fifths you will reach all twelve keys. Descending by fifths is the same as ascending by fourths. If you begin with C major there are no sharps or flats. F Major has one flat. G Major has one sharp.

Enharmonic equivalents, such as G# sounding the same as A flat, have the same pitch, but are written differently. They show relationships and one may be easier to read or think about than another.