“Thanks” is all of these:

a noun meaning “expression of gratitude,” as in,”We give thanks for our riches” ;

an informal exclamation meaning, “Thank you,”

the third person singular of the present tense of the verb “thank.”

The only possible uses of “thank’s” would be these:

a contraction of “thank is,” as in “The person to thank’s not here right now”;

a contraction of “thank has,” as in “The person to thank’s already left the party”;

the possessive form of the singular noun “thank” —- but there is no singular noun “thank”.

In short, you use “thanks” many times every day, but may well have gone your whole life without ever saying or needing to write “thank’s.”