Hey, everyone. Im very confused. Ive built older PCs, but none with external bays, and the whole concept confuses me.

I own a Gateway FX6850-47C that I bought last year.
Specifications of it are here: NOT ALLOWED TO INCLUDE LINKS - NEW USER

Question is... is there a way I can add USB 3.0 to my system, as Im not familiar with the technology. Maybe through the PCI slot? That possible?

And also, these external bay drives I have... (I believe some are 3.5" and another 5" or so), can I just pop a hard drive into them and itll work? Like, why is it external? Has to be some reason... because I really want to include more space into my system internally without having to really open up the machine, so I was wondering how to utilize my external bays. Im hoping its just pop in and were good, but I have a fishy feeling thats impossible?

Im trying to find more information regarding my system but it was recalled and replaced a few months after release due to the ATI card and drivers having major issues and causing mass returns(I got by it though by installing old revisions of the AMD/ATI drivers and an older revision of Catalyst Control Center to expand my second monitor, but its still a bitch installing a new OS and wishing and hoping it will work).

Please inform me on what it is I am capable of doing. Basically, these are my specs, and I want USB 3.0 and want to install more disk space, and if its possible, through my external bays.

Thank you to everyone who has taken the time to help, read, and respond.