The UI is a design, not a random set of forms. You need to layout the UI, define all elements that will go into each screen, and also define the flow from screen to screen in a multi-screen application. Every screen in your application is also in the documentation. You do not need pictures of each, but you do need;
- Data elements on the screen
- Necessary order of each element
- Interface elements on the screen
- Connections to other screens
- Functions of the elements (add, edit, delete, set access,…)