Outboard just refers to not inboard or onboard. It doesn't have to do with the direction signals go.
For instance, in a pc, you may have reverb in your recording software. That is an onboard effect. If you don't like it, or want something different, you can buy a nice hardware reverb, and patch it in to your pc to use it. That is an outboard piece of gear. Send your signal out to the reverb, and back in to your pc. How you patch it in is going to depend on your existing hardware, and may require you to buy something new.
I'm not too hip on computer soundcards and hooking them up. Post a question about hooking up outboard gear in computers and soundcards. List your gear and software and someone should be able to help.