ok, your telephone wire has 4 wires in it. two is for grounding, one is for data and the fourth is for voice. what happens is their is a modulator demodulator called your modem. what this does is encode the data being sent out of your computer and turn it into voice.
next after your modem translates the data into voice, the telephone wire is used to transmit the voice signals. then when the voice signal reaches another computer the modem decodes the data, changing the voice signal into data which the computer can understand. and the process is repeated for every computer that has to send and receive the information.
think of it as a phone call. when you talk, your voice is sent to a speaker which translates the voice signal into audible content which the person on the other line can understand.
when you check out your porn sites (nothing is wrong with that, its nature) or sites like this, your computer sends data to a server requesting information, then the server sends the data back to your computer utilizing the method i mentioned above.
do you understand how you access the internet over the wires??
any other questions, just ask em.