Whether you apply online or by mail: Your application is always the key to a successful career change.
The application - including the cover letter and letters of reference - is initially the only thing your potential employer knows about you. Consequently, your application should be done in a way that gives the reader a good idea about your qualifications and interests.
Every application is something special and personal. It must be orderly. It must be well-structured, and it must be complete.
Your cover letter should concisely provide the most important information: Which position are you applying for? Why are you interested in the job, and what are your expectations? And why are you especially qualified for the job? Your resume should be written in a tabular form, beginning with your latest employer.
Your application should include a cover letter, a resume and important letters of recommendation.