For 2,3-butanediol, there are 3 isomers; 2 are enantiomers, one is not. Use Fischer projections and draw all three. Identify stereocenters and identify them as enantiomers and the meso compound.
The meso compound can be shown with either both -OH groups on the right of the Fischer projection, or both on the left:
This solution provides a brief response, including diagrams to show the meso compound in a Fischer projection.