Hi Sara,
> I already made a post about where my data will be hosted when using WAB (DE) and the answer was 'on AGOL'
Apologies, I misunderstood what you posted. Yes, you can use Web AppBuilder Developer Edition with your ArcGIS Online organization with your data hosted in ArcGIS Online.
I made this statement,
> You can use web services from your own ArcGIS Server site - which can be referenced as items in ArcGIS Online or directly referenced in a web map
because I thought you wanted to use data that was hosted on your own ArcGIS Server site. In this case, you would register the web services with ArcGIS Online, see this help topic:
Add items—ArcGIS Online Help | ArcGIS
(look under the Add items from the web section)
But since you're storing your data in ArcGIS Online, this does not really apply.
> about my sentence 'adding items with properities to shapefiles', as an example, I have a layer of students (name, class, school,...) and I wanna add students using my app with their names, class and school ..
It is possible to add your student data (saved as a shapefile) to ArcGIS Online and you can create a hosted feature service. Then you can enabled web editing on it - Web AppBuilder has 2 edit widgets for you to use.
Hope this helps,