My teacher had told me that "it's kind/nice of you" is an expression of praising but I have heard this phrase from others as an expression of thankfulness.Which one is correct?
It has both meanings of praise and thankfulness
That's very kind of you
That's very nice of you
That's very thoughtful of you
That's very sweet of you
often accompanied by "thank you"
Thank you, that's very kind of you.