Thanks for posting on GeoNet! ArcGIS Experience Builder is a platform where you can create web applications using your data. You can also use these templates as mobile apps as well. Many users who want to convey information spatial (e.g. a web map) or non-spatial information in an accessible form like to utilize ArcGIS Experience Builder. As an example, I'd recommend taking a look at the San Diego app, which is listed on our overview page (first link) under "Web apps reimagined". This is also a really great resource in general for learning more about Experience Builder, along with the documentation page, both of which are listed below:
By contrast, ArcGIS Hub is more so a community engagement platform, allowing users to share open data and websites or create initiatives, to name a few of its functionalities. For more information on ArcGIS Hub, feel free to view our resources here:
Hope it helps!