A simple application letter for the job can be written with the main focal point being your intention to get the job.
Apart from the to and from (receiver's and sender's) address, the letter must be divided into 3 parts - introduction, body, and conclusion.
The introduction must state where you heard about the job opening and your interest in working for that job.
The body shall answer the hirer the following questions. 1. Why do you want to be hired for this job? 2. Your educational qualifications 3.Your availability for doing the job right away.
The conclusion can be done by saying that you are looking forward to a positive reply. Your official CV/Resume, if attached to the letter, must be mentioned in the conclusion and in the end, the required salutations can be used.