Sometimes we make assumptions about things that aren't explicit in the question, but that can lead to confusion or bad answers. On the other hand we may know, by experience, that the OP question can be answered by assuming certain things that are common. For example, in this question the OP clearly states his current scenario:
Currently I only have a modem but no wifi, if I plug my ipod to my PC via the usb port, it still doesn't allow me to use the PC's internet.
On one of the comments another user said that, although the OP stated that there was no wifi on his PC, in his experience most users do have wifi even if they don't know it.
Is it ok to assume this as being true? Or should the correct procedure be to just answer the question that is being asked exactly as it's being asked without assuming anything else?