A resume is a self-marketing tool that summarizes a person's employability and qualifications to potential employers. It highlights one's strongest achievements and experience in a way that is tailored to their career objectives. There are two main resume formats - a functional resume focuses only on skills relevant to the job objective, while a chronological resume combines all work history in reverse chronological order from most recent to oldest position. The formats differ in how information is presented but both provide basic personal and employment details.