What do write in a thank you letter and when and to whom I should send one?

Answer 1

Do not over look the thank you letter. It can be very help full to make you stand out from other candidates. In your job search you have to make use of all the tools, and the Interview thank you letter is one of them.

Thank You Letter General Guide Lines
The letter has to be sent before the decision to hire a particular candidate has been made.
It is your last opportunity to mention any information you missed to mention in your CV/a>, Cover Letter or Interview.
Clear up any misunderstandings.
You can use some things you learnt during your interview to your advantage.
This shows you are a professional.
Your last opportunity to leave a good impression.
Send it within one day of the interview.

When to use a Thank You Letter :
After an employment interview.
To a person or contact who referred to a particular job.

Thank You Letter Structure
Short and Simple is the key.
Mention Specific points discussed.
Follow the how to write a cover letter guide lines.
1st Part Thank Interviewer, for time and interest.
2nd Part Emphasis skills, enthusiasm and why you are fit for the job. Mention also any new things you have learnt about the organisation.
3rd Part Provide your contact details, and any follow up action.

Have a look at the sample thank you letter.

In all cases make sure you follow the Guide on writing Job related Correspondence which gives a lot of specific tips on writing different types of Cover Letters.

from http://www.cvtips.com/interview_thank_you_letter.html

Answer 2

There are sometimes that it may not be necessary to send a thank you, but you can anyway. Generally, the rule is that you don't have to send a thank you if you told the person thank you in person.

The general form for a note is:

Dear Aunt Sallie,
Thank you for the wonderful sweater you made for me. It looks wonderful with my favorite jeans, so I will be wearing it often. You must have spent countless hours knitting, thank you for going to such trouble for me. I am sure I will spend many days enjoying the warmth it gives me, especially in my heart!!

Sincerely,
Katie

So there is an example. Good luck!