Can I use another motherboard add extra RAM, Hard Drives, Processors, etc to my laptop, linked through the Expansion port?

If so, how?

no

Many laptops have a docking station designed for them- although these usually just add extra ports and cdrom drives (and sometimes a hard drive).

A lifetime ago, you might find some that also included things like ram upgrades, or extra fans so that it were safer to run the CPU faster. These days, you can usually get some extra usb ports which you can put flash drives in and use for swap/pagefiles.

ok, how about desktops?? this topic is interesting.

No.

Closest thing you will get is clustering several independent computers together over a high speed link (InfiniBand).