Do you have below questions in S/4HANA Marketing Cloud?
1. How do I add fields to different business contexts like Segmentation, interaction contact etc. ?
2. How do I make my custom fields visible for segmentation?
3. How do I add custom table to the system?
4. How do I use my custom table in Segmentation?
5. How do I make my custom fields and custom tables available in my Production System?
You can find answer to these questions by referring to this step by step guide: Segmentation Extensibility in SAP S/4HANA Marketing Cloud.