Which finger are you going to use for the first note "C quater" ? You use your righthand's thumb. Oh my God! There are a few clavier works for practice which encourage the use of your left hand. Your left hand have to be awaken up. In this fugue the left hand first. It is like escorting a lady by your left hand. If you practise the violin, your left hand has more important role than your right hand. Why not for the clavier? In the first bar all five fingers of your left hand have to work naturally. Anyway this is a fugue with four voices. It is not easy for playing compared with the first prelude. And the theme starts on C Major and is afterward developed on several Major and minor keys. Accidental shraps and flats are following as the changes of keys. Or the first note of the recurring theme decides the key for the following bars. All these keys are mixed up and we can identify them only vaguely. But you have to find the meaning of each accidental sharp, flat or natural clearly. It is convenient for you to study it because this is on C Major key and basically you use white keys on your clavier. All black keys which you use are out of C Major scale.