Plug the phone cord into the wall outlet and the DSL modem. Plug a network cable (cat 5e) from the DSL Modem to the Network Card or the motherboards onboard net. Thats it for the hardware install. Unless you have a router or switch installed. In this case you just connect the cat 5e cable from the modem to the port on the router/switch that says something about connection for modem. And another cat 5e cable from the computer to one of the numbered ports on the router/switch.
Software, usually you just install the DSL software you get with the modem or phone company.