2-butanol is a clear, organic, secondary alcohol. That means the hydroxyl group is attached to the second carbon atom. The difference in the R-2-butanol and the S-2-butanol has to do with the positioning of the hydroxyl group on the second carbon atom. The R group has the hydroxyl group leaning forward in a three dimensional model, while the S group has the hydroxyl group receding, leaning in a backwards fashion, in a three dimensional model.
The two forms of butanol are chiral enantiomers of each other, meaning they are non-superimposable mirror images of each other. They are also optical stereoisomers, meaning they are the same chemical composition, but with a different placement of the atoms, the key difference being the positioning of the hydroxyl group. The center of the group is asymmetric, having four carbon atoms, with the hydroxyl group on carbon atom two. Both versions of the stereoisomers are found in equal proportions, making them a racemic mixture.