In a multi-vendor X-Cart store, new sellers can apply for vendor accounts via the vendor registration page available via the "Become a seller" link on the storefront. Before anyone applies for vendor accounts via that link, the store administrator should adjust the contents of the vendor registration page and the set of form fields that prospective vendors must complete. You can do this via the "Vendor Registration Form" page of your store Admin area (Store Setup -> Cart & Checkout).
The store administrator can change the welcome text to be displayed on the page and specify what information fields to include in the vendor registration form. They can also set the required fields for completion by prospective vendors.