SharePoint hub sites help you meet the needs of your organization by connecting and organizing sites based on project, department, division, region, etc. making it easier to:
discover related content such as news and other site activities,
apply common navigation and branding across associated sites,
search across all associated sites.
SharePoint administrators determine how many hub sites can be created in your organization and who can associate sites with each hub site. Sites associated with a SharePoint hub site will have a hub site navigation bar added to the top of the site, the look of the site and any site design features such as additional navigation links, applications, or custom lists with specific columns will be changed or added to match that of the hub site.
For help planning hub sites, see Planning your SharePoint hub sites.
Some functionality is introduced gradually to organizations that have set up the targeted release options in Office 365. This means that you may not yet see this feature or it may look different than what is described in the help articles.
At the top of a hub site and any associated sites, above the site navigation, is the hub site navigation bar. If you are the hub site owner, you can customize this navigation bar with links that make sense for your hub site and associated sites.
Search across the hub
When you search from a SharePoint hub site, content on the hub site itself along with content on any associated sites is returned in the search results. Users will only see content for which they have access to.
Recommended web parts
When a SharePoint administrator creates a hub site, they're essentially converting an existing SharePoint site to a hub site. A hub site navigation bar appears at the top of the site, but the home page and all site content remains the same.
To get the most out of your hub site, the site's owner can add the following web parts to the home page:
News published on a hub site and on any associated sites is automatically aggregated and shown on the home page of the hub site by using the News web part. You can choose which associated sites display news on the hub site home page and users will only see news for sites they have access to. Clicking on a news article link takes you to the site on which the article appears.
Display the most active sites associated with the hub site on the home page by using the Sites web part.
Use the Highlighted content web part to dynamically display content from sites associated with the hub site on the home page.
Hub site security
Sites associated with a SharePoint hub site don't inherit the permissions of the hub site or any other sites associated with it. Each site, including the hub site, will retain their current permission settings.