I'd start here:
http://server.arcgis.com/en/server/latest/get-started/windows/what-is-arcgis-enterprise-.htm
This will give you an idea of the new "branding"
Then on the left hand side, go to the info on the new Enterprise Builder
This might help you out a lot.
http://server.arcgis.com/en/server/latest/get-started/windows/arcgis-enterprise-builder.htm
I have not used this but it looks very promising.
Enterprise is a complicated system.
Using ArcGIS Online (AGOL) is a much better solution if you don't have the support or experience to build up a network of servers, etc...
If you don't have a really good reason for your own Portal, let Esri do the work for you and use AGOL.
ArcGIS Enterprise (basically rebranded Portal, AGS, DataStore & Web Adaptor at 10.5) is awesome but you need an IT staff experienced with Esri servers to support it.
Or be prepared to start learning a lot.
The new name does say it all.
This is an Enterprise solution and that's a very different game than even what most people think of as Client/Server.
My 2 cents anyways.
-Paul Davidson
