This beginner's section on Ports is work in progress, but the larger trail already has a lot on more advanced port-related topics. Please visit also here: 09:03: Port conjugation in SysML is now Type-based
This topic is covered in the course: Course: Model-Based Systems Engineering with the OMG's Systems Modeling Language® (v1) and the MagicDraw/Cameo (CATIA Magic™) tools for SysML
There's lots about Ports in these online trail sections:
And this site is full of rich examples about using Ports for modelling signal processing, flows, and physical interaction. Try searching by keyword: UML Port, SysML "standard" Port.