If you have many sitemaps, you can use a sitemap index file as a way to submit them at once.
The XML sitemap generator extension creates separate XML sitemap file for products page links, categories page links, informations page links, manufacturer page links. All these separately created XML sitemap file are referenced in the index sitemap file. Therefore when you are submitting the sitemap, you only need to submit the sitemap index file. All other sitemap files are referenced in the index file.sitemap, xml