Hi, modules are to show content from components or to show content from itself. If you want to manage advertisement on your website you have two options: 1) Use default Banner component and modules (but it has weak features) 2) Use additional extension for example: FlexBanner or AdsManager (check if version for J3 are available)
But if you want to create catalog, for example with car / motorcycle parts you have to use : K2, MTree, redLIST or SobiPro. They include components and few modules.