The two structures shown (left and right) are butan-2-ol drawn with opposite wedge patterns at C2. They are related as

Butan-2-ol has one stereocentre, C2, which carries H, OH, $\mathrm{CH}{}_3$ and $\mathrm{C}{}_2\mathrm{H}{}_5$. The two drawings differ only in the configuration at this single centre: one is (R) and the other is (S). A molecule with one stereocentre is chiral, and inverting its only stereocentre gives its mirror image, so the two structures are a pair of enantiomers.