Orcad to Kicad schematic
Kicad global connector is valid for whole schema project (all sheets), hierarchical port provides connector on hierarchical sheet. It makes significant difference if your  hierarchical sheet is reused more times or you have own library of sheets. In this case you can connect hierarchical connector on project sheet where hierarchical sheet(s) is/are placed.
It's analogous to programming: global variable vs. procedure with arguments.
You should be able use proper connector when you understand topology of your Orcad scheme.