Talk to your teacher or principal about your need for a letter of recommendation. You can do this in person if you are still in school, but if not, send an email. This will allow them to process your request at their convenience and allow them to reply with ease.
Receive an affirmation from your principal or teacher that they are willing to help you in your application process. Search through your online application and find the section for letters of recommendation.
Under the letters of recommendation page, submit the email addresses of the principals and teachers who have agreed to write you a letter and click submit.
Check with your teachers via email to see if they received an invitation to submit a letter of recommendation for you via email. If not, contact the school to see if you can re-submit their emails or if the school can handle the request for you.