Many persons like to set up their Internet connections right next to their computers. In the case of DSL, you would need to have a telephone connection nearby to set up the DSL modem, and sometimes there isn't a telephone jack nearby.
Wiring a telephone jack is relatively simple. If you have an unused telephone jack (such as a wall jack found at most home improvement stores), a spool of four-wire telephone cable, a screwdriver and a pair of needle-nose pliers, you can make an extension of your single-line telephone service.
First, install the base plate of the wall jack on the wall closest to where your DSL modem will be set up. A wall jack will typically have the mounting hardware necessary (such as screws and covers) to attach the jack to the wall.
Next, run a length of telephone wire from the nearest active telephone jack to the new wall jack. Make sure to leave about 6 inches of slack on each end of the telephone wire.
After that, go back to the new wall jack, and strip away the top layer of insulation from the first inch or so of telephone cable. This will reveal four smaller wires - one red, one green, one yellow, and one black. On each smaller wire, strip away about 1/4 inch of insulation, exposing about 1/4 inch of bare wire. Make a small "hook" out of each the bare wires (taking care not to break the individual strands).
Next, install each colored wire to each marked terminal. Red wires should be connected to the "red" marked fastening screw, green wires connected to "green" marked screws, etc. Once you are done installing the wires, make sure each connecting screw is tight and there are no loose wires. Install the telephone jack cover on the base plate, and make sure that the cover is fastened securely to the base plate.
After you are done installing the new phone jack, go to the active phone jack that you are extending phone service from. Strip away about an inch of the top insulation layer to expose the four colored wires. Repeat the steps outlined above, making sure that your existing telephone wiring makes a physical connection at the bare wire to your extension.