what is hams? how to applied it?

what is hams? how to applied it?
Hams is an Arabic word- , which by definition means whisper.  In applied tajweed it is the running of breath done when pronouncing a letter in opposed to imprisoning the breath.  For example in the letter , if pronounced properly, you will hear air running with it. 
This can be compared to the opposite of this in the letter , in which there can be no air running while pronouncing it, if pronounced properly.

The letters which have are the letters found in the group:

One needs to not completely close off the articulation point of the letter, so that there will be a place for the air to flow.  This is done by lightening the pressure on the articulation point. 
And Allah knows best.