The Submission Accounts module comes with its own pre-built login page. This looks and functions almost identically to the main Form Tools login page, except that it's slightly more customizable in terms of the text you see listed (labels and text). See the Settings page for more information about the customizable settings.
In order to use the login page, you MUST pass the relevant form ID to the page via either the query string or a POST variable. For example, here's a direct link passing it via GET:
The form ID is required (in the example, X would be replaced with your form ID). It's used to let the module know which form is needed. The script checks it's valid before displaying the login page. The styles of the login page depends on the form ID - when you originally configured you form, you specified a theme. That's what's used here.
Lastly, if you specified an email field for your Submission Account, a "Forgot your password?" link will appear, providing the user with a little fallback in case they lost their password.