Your laptop needs to have a modem to be able to call. The landline should be attached to the RJ-11 connector. You can see the image below for an example.
On the right side:
- RJ-11 connector - the one on the left (landline cable)
- RJ-45 connector - the one on the right (LAN cable)
If you don't have a modem, visit your local IT store to buy one.