Lets start with first set:
Ka Kha Ga Gha
क ख ग घ
Ignore ङ् for now.
In Tamil, we don't have Kha and Gha.
And Ka and Ga have same letter க
So we just need to know one க for 4 alphabets!
Visualize a straight line coming down and then looping up to CUT itself and then coming back. All this travel to CUT itself. Hence க is Ka (Pronunciation of CU in CUT)
क ख ग घ comes then it is ङ
च छ ज झ then ञ
ट ठ ड ढ then ण
त थ द ध then न
प फ ब भ then म
Concept is to pronounce Na in a way that least movement of tongue is needed.
For Ka group it is ங in #Tamil or ङ in Devanagari
See, 3 lines and a Fat Nose (NaaK in Hindi) between two lines.
Remove vowels and pronounce NK together. The kind of N you pronounce is ங
Tamil does not have Chha and Jha. And Cha and Ja are represented by same letter. Even Sa is included because Cha and Sa zones are close in palate. (Even in Asamiya I think it is same)
The alphabet is ச which is க without tail
Tamil doesn't have Dha and Tha
Ta and Da given by ட
Looks like a broken T fallen on ground.
Hence T (Tree), D (Doll) given by ட
It is a spriNg attached to T. In Bangla, Devanagari also Na is given by न ন .
The Na is elongated with more loops in Tamil and hence it becomes a deeper Na like in Danda, Bhandaar unlike in Bandar.
Congrats. You now know 50% #Tamil alphabets!