Sanskrit Letter in Tamil Alphabet

There is 05 letters that are originally from sanskrit and are used in Thamil. (most of times hadly used )
they are :

ஷ - sha. This letter has the sound of sh as in shut. Sometimes instead of using the Sanskrit letter, its used the Tamil letter ட. Ex. :  நஷ்டம்(nashtam) - நட்டம்(nattam) means loss.

ஸ - sa - Has the sound of s in sun. for example, புஸ்தகம்(pustakam)- book is sometimes written in pure Tamil as புத்தகம் (puththagam).

ஜ - ja. It has the sound of J in jug. In Tamil most of times the letter used in the place is ச(sa/cha). ஜனம்(janam-people) is written as சனம்(sanam)

க்ஷ-ksha. It is combination of ka and sha. The Tamil letters used in its place are ட்ச. மோக்ஷம்(moksham-heaven) is written as மோட்சம்(motcham)

ஹ-ha. h as in hut. Mostly, in names having ha it is replaced by ka/ga.  மனோஹர்(Manohar) is written as மனோகர்(Manogar).

* examples of pronounce are taken from : Language Reef. * 

Most of times it is used in hindu gods and goddess name,some examples :
லக்ஷ்மி = Lakshmi ( Hindu goddess of wealth )
கிருஷ்ணா = Krishna
சரஸ்வதி = Saraswathi
விஷ்ணு = Vishnu