In terms of comparason A web app and web form are totally different things.
A web form is a form you can build to submit information of the person and any custom data you create Into the CRM of Business Catalyst. The person is created if new or if existing the information from that form attached to that person. The information of that form is stored into a Case agaisnt that person. Web forms can be used to sign people to secure zones, set people as wholesalers, place them on a campaign list, populate custom CRM fields and more.
A web app is a custom web application. If you want to build anything from a listing of houses of information which has a detailed page of that house, to testimonials to what ever you want. With the layout output options and custom fields you can create you can build all sorts of things. Know something like jQuery very well and you can build some relaly cool things.
This is primarly a means to output a lot of data items.
A web app also has the ability for logged in users to add items and edit items associated with them IF you set up these features of the web app when you create it. A public profile for example that person can edit or submit.
The information created as web app items are not part of the CRM so you mentioned users uplading images and a description, the web app item information there is not stored agaisnt the person in the CRM.
Ok thanks I got that cleared on this . . .