The most important used namespace containing the base building blocks for your module are contained in DotNetNuke.Entities.Modules. 

PortalModuleBase

For the screens build for your module (module controls) the PortalModuleBase is inherited.

Here you see an example for the Module ViewWerknemers that inherits the PortalModuleBase.

The PortalModuleBase class defines a custom base class inherited by all desktop portal modules within the Portal.  The PortalModuleBase class defines portal specific properties that are used by the portal framework to correctly display portal modules.