Yours sincerely is used if you don't know the name, yours truly if you do. Best regards (many people use Regards) are for less formal letters eg in the case of the neighbour if you don't know him very well. You write them at the bottom left, before you sign your name below. If it's a more formal situation then write your whole name.
If you have access to any student's manuals, check to see if there is a Writing bank at the back of the books - they are usually quite clear and helpful.
By the way, especially since you are preparing for IELTS, it's a good idea to use 'your', 'please' etc in these forums since there isn't a price on the characters.
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