There are a few options available. For hiding cables under or behind the desk you can use something like a J Channel or a Signum from Ikea. To have a cleaner look for the cables coming from the PC you could simply bundle them. Something like a Cable Flex wrap or cable sleeve you may find helpful. Hope that helps.

raceway for tv cords Cable clips Velcro cable ties Cable sleeve Cable drops Another type of raceway

Those are some things ive used. ive added pics of my setup and how ive used them. honestly the best way to find ideas is just look up Desk cable managment in youtube and watch some videos thats how i got some of these ideas! Hopes this helpds man