Here you can choose to create a new product or product section. Select the required type from the product or section type lists (if available) and open the new product or section editing interface. Please note that product and section types can be managed in Site Manager -> Development -> Document types, as described in detail in the Document types and transformations chapter in the Development section of the Developer's Guide.
The Link an existing product or section button allows you to create a linked product or section, which will be a shortcut to an already existing product or section.
More resources concerning product types and section types can be found in Products -> Product types chapter in the Managing your store section of the E-commerce Guide.
Further information about products can be found in E-commerce Guide -> Managing your store -> Products.