Breadcrumbs are text navigation threads often placed at the top of web pages. They allow users and search engines to follow the site structure related to any given page. Why are they important to SEO? Done properly, they make it easy for users to navigate throughout your site, and in turn, they communicate your site structure to search engines. Both very, very good things.
Breadcrumbs should always start with your homepage, then list the current category, and post name. If a given page is listed in multiple categories, pick the most popular – don’t have duplicates, as this gets too confusing.