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. 
[![enter image description here](https://i.stack.imgur.com/oN2e3.jpg)](https://i.stack.imgur.com/oN2e3.jpg)
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:


[![enter image description here](https://i.stack.imgur.com/OzJv2.png)](https://i.stack.imgur.com/OzJv2.png)
[![enter image description here](https://i.stack.imgur.com/bU92R.png)](https://i.stack.imgur.com/bU92R.png)


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


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