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Your module can get a "Configure" link in the back - office module list, and therefore let the user change some settings. This "Configure" link appears with addition of the getContent() method to your main class. This is a standard PrestaShop method: its sole existence sends a message to the back - office, saying "there's a configuration page in this module, display the configuration link".
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HelperForm is one of the helper methods that were added with PrestaShop 1.5, along with HelperOptions, HelperList, HelperView and HelperHelpAccess. They enable you to generate standard HTML elements for the back - office as well as for module configuration pages.
You can get more information about Helper classes in the "Helpers" chapter of this developer guide, with a page dedicated to HelperForm.
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