When we learned Nepali in School the letters श transliterated as Ś and ष transliterated as Ṣ was either pronounced same or ष was pronounced as ख.

In the below two words the transliteration is different.
ऋषि transliterated as ṛṣi vs शीतल transliterated as śītal

So how are we actually supposed to pronounce these two letters differently?

Trying to see if any sajha Bidwan has idea/knowledge about pronounciation and can explain for those two letters.

ष and श

The difference between श, ष, स is mainly based on the position of tongue while pronouncing. It can get tricky and many school teacher don't even know the difference.

श (Ś) is palatal meaning the position of tongue is in the palatal region. Also, a gush of air which is called 'aspiration' comes out while pronouncing श. Example: शान्ति

ष (Ṣ) is cerebral meaning the position of tongue is cerebral. The back portion of the tongue touches the very back portion inside the mouth. Example: विष्णु

स (S) is dental meaning the position of tongue is close to the teeth. Example: सरस्वति

By becoming aware of the level of stress the tongue puts while pronouncing, one can easily distinguish the difference.

Thank you ujit,

That was helpful. I basically understand the श sound but when I tried to sound विष्णु with the back portion of the tongue touches the very back portion it sounded like lato le bole jasto.

Is there a youtube video or any audio with correct pronouncation for the ष sound?