"thank" is a verb for when you appreciate something: "He helped you a lot today. You should thank him." Or when something in responsible for something: "We can thank him for getting on in this mess." ----- "thanks" is an interjection, meaning "thank you" but more informal: "You helped me a lot today. Thanks." Or a noun: "I helped you a lot today. Is this all the thanks I get?"

"Thanks" is a more casual version of "thank you". You should never just say "thank" on its own. "To thank" is a verb, and you can use it in a sentence.

thank = thank. thanks = thanks a lot. So, as you know, if you want to thank someone deeply, you should use "thanks" example: Hi, Tal, I am glad to have your answer, thanks. ^_^

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