Whether you upload your files using ProductionPro on the Web or the ProductionPro iPad app, you'll find your untagged files by tapping "Untagged" at the bottom of the class drawer. The number next to the icon will tell you how many files are untagged.
To tag your files:
Tap "Select" in the upper right corner of the library space (under "Current").
Select which files you want to tag and tap "Edit Tags" in the upper right corner.
Assign the Character, Department, Scene, or other production tags you'd like to use in the pop-up window.
Once you've assigned tags, the files will disappear from the Untagged space. You can return to the current library space by tapping "Untagged" once more to view and filter those files, or you can view them in the Visual Scroll.