The Fischer formula is a means to represent the spatial configuration of a sugar or amino acid and related. Representation and rules:

It is often simplified by leaving the asymmetric carbon aside:

The vertical bonds point in reality towards the rear, the horizontal ones towards the front;

Depending on the position of the amino or alcohol group on the left or on the right on the horizontal line, we have the enantiomers L or D. Example

Enantiomer D