Hello, I asked a question on the Q AND A website and got an answer, and that led me to sort out the problem that I had, and since the person helped me I want to tell them how much they have helped me but when I asked the question I was only a guest and now I have an account so I don't think that I can tell the person that. They were called "Ahab Greybeard "
Could you please tell me a way to thank them because I would like that.
Thank you

That is quite easy, He has an account here with the nickname "ahabgreaybeard". There are several possibilities:
* do it publicly by rating him. Just go to a post where he wrote or answered and click on the karma number under his name. You will be led to a new page where you can rate the user. Of course you can also thank him in commenting on a thread where he wrote.
* in private: by sending him a private message: Click on his avatar and you will be sent to a new page where you can write a private message. He will be immediately notified the next time he logs in.