Ports export nets from a module to the higher-level schematic and define connection points for wiring signals. Modules organize hierarchical schematics by creating sub-designs on separate sheets. When you add a port to a module, it is automatically labeled and appears on each instance of that module.
Each port has a name and a direction. The direction defines the signal flow for the Electrical Rule Check (ERC): io, nc, in, out, oc, pwr, pas, or hiz.