Someone said Anunasika is like trying to say something entirely in nasal voice. So let’s say I want to pronounce a vowel ‘U’kara with Chandrabindu on top of it. I know it’s should be completely a nasal sound. So based on my understanding it is to be I pronounced with my mouth formed as if I’m trying to say the vowel U but sound should mainly come out of my nose and little bit in mouth. Is it correct??
Anunāsika is the Sanskrit name for what linguists call vowel nasalization. A vowel marked with a chandrabindu is pronounced with the soft palate lowered, allowing air to escape through your nose.
It's difficult to describe nasalization in text, but it's characteristic of French: in standard Parisian French, a vowel followed by a (silent) n or m will be pronounced nasalized, e.g. un vin.
You can also test if you're pronouncing a nasal vowel correctly by closing your mouth while saying it. If it turns into an /m/ sound, that's a nasal vowel.
This paper by Cardona surveys the problem of determining the status of anunāsika versus anusvāra (I don't derive any firm conclusions from this, but it does lay out the textual facts). Pāṇini is said to have believed that the terms refer to different phonetic things, and Whitney thinks the difference is terminological / theoretical without basis in reality. Aṣṭādhāyi Bk.1 Ch1. Sut.8 says, in typical telegraphic style, "mukhanāsikāvacano 'nunāsikaḥ", which Vasu translates as "that which is pronounced by the nose along with the mouth is anunāsika...". In addition to vowels, which may be nasalized, /n+l/ undergoes regressive lateralization to give [l̃l], which is also anunāsika. So the term may refer to nasalization of vowels and approximants. From a practical perspective, making a nasalized vowel is sufficient, until you decide to dig at a high level into the terminology.
You should check out this link: https://www.quora.com/What-is-the-core-difference-between-Anusv%C4%81ra-%E0%A4%85%E0%A4%A8%E0%A5%81%E0%A4%B8%E0%A5%8D%E0%A4%B5%E0%A4%BE%E0%A4%B0-vowel-and-Anun%C4%81sika-%E0%A4%85%E0%A4%A8%E0%A5%81%E0%A4%A8%E0%A4%BE%E0%A4%B8%E0%A4%BF%E0%A4%95-consonants
I will paste it here:
AnusvAra as the word itself explains is "giving voice to" following the vowel, the full and complete pronunciation of म् in अम्, कम् etc.,
In anunAsika the term tells you that it is a letter-pronunciation that is aided by the nose. Consider the Panini Sutra मुखनासिकावचनोऽनिनासिकः (पा.सू.1-1-08).मुख-नासिका-आवचनः = मुखनासिकावचनः सः अनुनासिकः | This is the definitional sutra for anunAsika. The standard explanation goes thus. मुखसहितानासिका= mouth(the oral cavity) together with the nose(the nasal column) ईशद्वचनम् आवचनम् = slightly pronounced. That means the anunAsika which represented in scripy by chandra-bindu the vowel must be nasalized. In fact in Paninian Grammar the nasalized vowel is one distinct entity in 18 basic forms of vowels. Thus the vanrgAnta(last letters of the vargIya-vyanjanas are the anunAsikas referred to by the pratyAhAra-sutra ञमङणनम् | This sutra collects all the anunAsikas together. These letters singly are best pronounced and correctly so by Malayalis. In snadhi formed usages like भवाँल्लुब्धैः(=भवान् + लुब्धैः) the long vowel आ is just nasalized. Whatever you have written about the representation of anuswAra in script if correct and in line with Panini's recommendations. How should the anuswAra in संस्कारः, संस्कृतम् be prononced? For in places where the anuswAra is followed by a vargIya-vyanjana the "process" of pronunciation "naturally" forces you to correctly pronounce the auswAra rightly. It is when anuswAra is follwoed by non-classed consonants that you get into trouble. You can see a variety of pronunciations of the anuswara in thses cases. It varies from pronouncing it as न् in northern states, somewhat like औँ in Maharashtra and North Karnataka and as well-intoned म् down south(South Karnataka, Andhra, Kerala and Tamilnadu). Which is in line with Panini?
I would like to do that in an edit. Till then ruminate.