Mitochondrial DNA (mtDNA) is passed down from a mother to her sons and daughters. However, only daughters pass it on to their children. So, whether you or a man or a woman, you will have received your mitochondrial DNA from your mother's mother's mother etc (i.e. your direct female line).
Mitochondrial DNA can be used to connect with distant cousins on your direct female line.
It has a "reach" of about 200,000 years and thus can be used for exploring your deep ancestry on your direct female line. This will give you an indication of the route that your direct female line ancestors took when they left Africa during the last human migration.