Your database holds all of the information that you add to your site (except files).
When you add new content, pages, posts, plugins and other content, the text content and settings for these elements are stored in the site’s database.
WordPress databases can grow quite large over time, so it’s important to optimise them every so often to avoid slowing down your site.
They can also present themselves as a bit of a life-saver as they enable you to retrieve valuable data when you need it.
Where your database is stored is arranged by your hosting provider and acts like an address for your website information and data.