It is not necessary to write about every experience you have had. Select those you want to talk about. Do not worry about gaps in time. Experiences showing communication and organizational skills or group work and leadership are important to mention. When describing positions, start each sentence with an action verb.
Statements become accomplishments vs. job descriptions.
You may draw from experiences obtained during high school, though you will do this less often closer to graduation. These are narrative entries for you to use to highlight computer, language, and experience skills. There are help boxes within the system to help you write and organize your computer and language skills. The experience statement falls at the end of the Work Experience section on the resume. It gives you the opportunity to go into greater detail about yourself.