Hi Paintscraper, Welcome to the forum!
I am sorry, but I am not sure what you want to do?
- You don't normally have a midi port on the computer, rather on your audio interface or midi keyboard. Do you want to play drums via midi keyboard?
- Do you mean that you want to use drum samples saved on a USB stick in Session drummer 3? Yes you can do that. You can load your own samples to build your own kits. However I find this easier to do in Native Instruments Battery 3 or other drum software for that.
There are a lot of info in this forum and youtube.com
Good luck!