Customizing the User Menu
After configuring a new form for use with the Submission Accounts module, visit the main Submission Accounts page (click on the Submission Accounts link in the module nav menu) and click the Edit link for your form. There, click on the Menus tab and you'll see a page looking something like the screenshot to the right - only probably a whole lot blanker.
This page operates exactly like the main Admin and Client menu builder, found on your Settings » Menus tab. Here, you can construct a menu containing whatever items you want your users to see when they log in to edit their submission. Unlike the client and admin menu page, you'll see the options are quite limited! There are three main options: Edit Submission, Logout and Custom URL. You'll always want to include the first two. That lets the user be able to view (and potentially edit, if your View permits it) their submission information and log out when they're done. The Custom URL option lets you link to external pages, e.g. relevant pages on your website. The user will always be linked to the Edit Submission page upon logging in.
The Pages module
Another fun trick is to use the Pages module to create custom pages that you can include in the left nav. The Pages module was designed for exactly this purpose. You can enter documentation or information pages very simply through the UI, providing your users with whatever custom information they may require.