The Submission Accounts module lets you convert your form submissions into basic user accounts, allowing the people who originally submitted the form to log in and update their submission at a later date. This module can be used for as many forms as you want, and provides a fair amount of control over what information can be viewed and edited by the user.
In broad strokes, here's how the script works. When you first configure a form to implement the submission accounts, you need to pinpoint two fields within your form which act as the login username and password. Often, you may need to add an additional "password" field to your form to integrate it with this module. For the username, you can choose whatever field you want - but generally you'd pick the email field since it's a great way to uniquely identify the user.
Next, you'd pick a theme and a View. This determines both the appearance of the UI for the user when they log in, but also the fields that they can see and are editable.
Last, you'll need to link the user to the login form. For convenience, the module comes with its own login page (found here: /modules/submission_accounts/login.php) but it also includes a login form generation tool to allow you to embed your own login forms within your own webpages.
Now onto some more details!