The easiest way to do this IF your PC has a 3.5mm stereo headphone jack is to wire each speaker to an RCA phono male plug (supplier example only).
Connect the speaker wire with the black stripe to the inner connector of the plug and the other wire in the speaker cable to the outer connector of the plug.
Do this for each speaker i.e. each speaker will be connected to its own RCA plug.
Here's a video that shows how to wire an RCA plug that may help.
Then you will need to use a 3.5mm stereo plug to double RCA jacks adapter (supplier example only) to connect the speakers to the PC.
Simply plug each speaker into the adapter and then plug it into the PC's 3.5mm headphone jack.
The volume may not be the loudest as usually headphone outputs aren't too loud, so as to protect the ears.
If your PC has a sound card with RCA type L & R audio outputs (or perhaps the motherboard may have this on the back panel if the audio is integrated) you can plug the cables directly into the PC without using the adapter.
The USB option isn't possible as it would mean installing a USB controller plus associated components (pcb board needed which would fit inside speaker) and cabling etc in one speaker and then daisy chaining the two speakers together to make it work. Really it's not worth thinking about.