In previous releases, once you create a plant, you have to activate MRP for this plant via customizing path: IMG -> Production -> MRP -> Planning File Entries -> Activate MRP and Set Up Planning File or transaction code OMDU.
However, in S/4 HANA, this customizing path does not exist any more. 
For S/4 HANA it is decided that all plants are by default relevant for MRP. Technically this means that T001W-BEDPL='X' is always set for each plant. For S/4 HANA Cloud, it is set from SAP. For S/4 HANA On Premise, please use the workaround to set relevant flags in t-code OMDU currently.
Also, you can see the customizing path Convert Planning File Entries for MRP Areas does not exist in S/4 HANA either. In S/4 HANA, the report RMDBVM00, RMDBVM10(for conversion MDVM/MDVL into DBVM/DBVL and back) is not available any more.
Do you have any other question about the MRP related customizing? Let's figure it out together one by one.