Separating Enantiomers
Enantiomers are mirror reflections, they have same physical and chemical properties. This like left and right hand.

Diastereomers have different physical and chemical properties. You can separate them on chromatography column or by crystallization.

In your example upper and bottom products are not mirror reflections.
Mirror relection of upper product looks like:




Just play with the 3D models in any drawing software to get the point.