ProMassMaintain is based on ProFramework.
The general ProFramework application is described in the AFW | ProFramework | User Manual.
The specifc widgets are described in Widgets for ProMassMaintain.
By default, ProMassMaintain can be started via one of the SAP transactions /PCH/MSM to /PCH/MSM9. These transactions can be assigned to corresponding ProFramework interface definitions via ProFramework Customizing.