In this case, you begin your cover letter with "I am writing to express my interest in the Manager position advertised on your website".
Try to avoid abbreviations (I'm, ok...) if possible and write the full words.
Question 3: To convince your potential employers that you're the perfect candidate for the position, you write...
a. I am the perfect candidate for the position.
b. As you can see, I rock at this job.
c. I am confident that my experiences make me an ideal candidate for the position.
d. I am ecstatic that my experiences make me the perfect person for the position.