Hi first make sure you have a wifi adsl router or just router.
if u have adsl wifi router then follow these steps

1. Switch on the wireless modem.
2. Plug your phone line into your  modem
3. Connect it with cable , insert one point in adsl modem and second one in your laptop.
4. Login to your modem control panel.
5. Enable the option of Wireless, you can also set wep key over there.
6. After doing all these.
7. Then make sure internet is working with that modem.
8. Remove your cable from your laptop.
9. Now you are conected to the internet through your wifi modem