The fist step when working with HubSite consist in a SharePoint Online administrator to register a SharePoint Online HubSite. You can do it from the SharePoint Online admin center under active sites :

You will be prompted to give the HubSite a Name, this is the name user will see in the Hub navigation bar and when associating a site. And optionally filter who can associate sites to this HubSite. If you leave it blank, everyone will be able to associate a site to this HubSite. When a site owner will try to associate his site to a HubSite, he will only see HubSites he has the right to associate a site to. Beware that he will get an error message if he has no access to the HubSite.

Once your HubSite is register, you configure it by navigating to the HubSite. A new menu appear when you click the configuration gear : HubSite settings

There you can change the HubSite Name, logo and site design applied to site when they join this hub. You can also edit the HubSite Navigation from the edit button:

Here are the related cmdLet for PowerShell using the Microsoft.Online.SharePoint.PowerShell module to register a SharePoint Online site as a HubSite :
#Replace Url with yours #Connecting to SharePoint Connect-SPOService -Url "https://btcstech-admin.sharepoint.com" #Register the site as a HubSite and filtering who can associate sites to it with the -Principals parameter Register-SPOHubSite -Site "https://btcstech.sharepoint.com/sites/NewHubsite" -Principals "john@mail.com" #You can put an office 365 group there #Register the site as a HubSite with no filtering on who can associate sites to it Register-SPOHubSite -Site "https://btcstech.sharepoint.com/sites/NewHubsite" -Principals $null #Editing HubSite properties (Name, description, logo and SiteDesign) Set-SPOHubSite -Identity "https://btcstech.sharepoint.com/sites/NewHubsite" -Title "My Hub site" -Description "This hub has a great theme and navigation" -LogoUrl "https://btcstech.sharepoint.com/sites/Marketing/Branding/HubLogo.png" -SiteDesignId "8ebf0cfc-52c0-4d2e-bd9c-3a8a86ab47cf"
You can find further information about registering a SharePoint Online site in the Microsoft documentation
See you soon in the blog section !