On OLAGE, we ask applicants to write a motivation letter or a cover letter for the chosen program. For what expectations ?
A letter of motivation (or cover letter) is a letter in which you describe your current background, your career plans and how the ESA expected program will help you in achieving your professional projects.
You can show your motivation and reasons for applying in accordance with this program and the skills you already have.
On Internet, you can find some templates.