Samy, that is correct. for Web AppBuilder you would need access to ArcGIS Online and/or Portal. However, if you have ArcGIS Server, and it is current on maintenance, you should already have access to it (talk with your customer service rep or distributor). With ArcGIS Online you have the option of using the online version of the Web AppBuilder.....or you can use the developer's version, once you create the appID on ArcGIS Online (or Portal). Check out a couple of my blog posts (one repeat of above...and messy posts, but lots of info):
Web AppBuilder Developer Edition - Customization Resource List
Tips and Observations for getting Web AppBuilder - Developer Edition Installed
With WebAppbuilder, there are many widgets that just need to be configured, or you can look into some of the user provided custom widgets that are available. But it can be fairly point-and-click if that is what you need. With the JSAPI, there are many samples, but you would be writing most from scratch.
ArcGIS API for JavaScript