If the PC has a built-in sound card, then a suitable cable to carry the audio from the Wavedrum to the PC line-in connector(s) will be necessary.
The colour coding for the line-in input is pink or red, though not all PCs follow this convention. There may also be an appropriate legend on the PC case next to the connector.
If the line-in connector is a 1/8" jack, then the chances are it is a stereo jack. What would be needed for this would be a cable with two 1/4" mono jacks at one end, to go into the wavedrum's L and R jacks, and with a 1/8" stereo jack on the other end to plug into the PC's line-in.
Generally speaking, the Wavedrum's volume will need to be set quite high in order for the output audio to match the input sensitivity of the line-in input. Since the headphone volume is also altered, this may result in an unacceptably high headphone volume, in which case a suitable volume controller may also be needed for the headphone lead.
As far as software goes, Audacity is freeware and relatively easy to use, and allows multiple tracks to be recorded, one stereo pair after another.