What is the true meaning of Kaya Sankhara, Vaci Sankhara and Citta Sankhara
Sankara is conditioning which puts together or makes or forms something.


Kaya Sankhara - this what sustains keeps the body together hence the breath. If breathing stops the body falls apart.
Vaci Sankhara - this is what sustains the formations of verbal throughs. Before speech thoughts need to form, without them one cannot speak. 
Citta Sankhara - this is what causes a mind to arise. Feeling and perceptions are what causes a mind to arise.


How this is relevant in meditation is given here.