Separating Enantiomers I understand that you can react enantiomers with a chiral molecule to resolve the enantiomers of interest into diastereomers. 

However I do not understand how exactly the added chiral molecule can make the enantiomers of interest into diastereomers.

Can someone please explain the process/mechanism ?

For example: here is a picture from my textbook. 

How are those two salts Diastereomers, even though they are mirror images of each other.
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.