When you edit or create new items in Sitecore, they must be published before they appear on your website. This lets you save unfinished items and decide exactly when the items are launched on the website.
When you work in Sitecore, the items you save are saved to the Master database. When you publish new items or updated items, the items are copied from the Master database to a publishing target, and from the publishing target, the website is launched. The default publishing target is the Web database.
You can choose to publish the entire website or a single item:
Site publishing – publishes your entire website starting from the root of the content tree. You can publish a site from the Content Editor or from the Sitecore Desktop.
Item publishing – publishes the item you select in either the Content Editor or the Experience Editor. The item can only be published if all its ancestors have been published. With item publishing, you can choose to include all of the selected item’s subitems and related items.