Thanks Giving Letter To HR

Dear Members,
I have successfully received the interview call from an HR outside the country.Now, i want to reply him to show the courtesy as they have considered me for the job.Is there any format regarding this?

hello mohsin,
i am new in this professional site. i think you only need to thank them for the opportunity given to you and promise to do your best in moving the company forward. please let me know the procedure for getting an oversea job like that. i am interested too

Dear Mr.Mohsin,
Do U wish to join them or U only wanted to pleasingly say "No thanks pl'". If U R not joining them simple thanks giving letter will do.
On the other hand if U want to join after selection in the interview there is no necessity to send a lengthy letter but simply acknowledge the receipt of the same and say that U would eagerly await to attend the interview and delighted to join them once U R selected.
All the best
kumar.s.