Store your documents, digital signing ceritificates and visual signature templates in one place and use them whenever you need. Your data gets securely stored using built-in iOS-encryption and never gets exposed unless you want to share it.
A tap on "Documents" gets you to the list of the groups and packages where you can manage the documents you store within the app. Swipe from the left edge of screen to reveal this menu or just tap a "hamburger" button at the upper left corner of the app window.
"Certificates" is where you add your digital signing certificates and "Signatures" is where you manage visual signature templates which you can use for documents signing if visual signature representation is needed.