Keeping track of your employment history throughout your working life is a good habit to get stuck into. It helps you stay organised and prepared for the future of your career, wherever it may take you.
Employment history can include anything that relates to work. You should be documenting your jobs, but also any volunteering, work experience and internships. That way, when you are ready to move on and look for a new job, or an opportunity arises, you are ready to go.