To start the configuration process, follow the instructions in the README file to properly install the sources. You start the kernel configuration process with...
In order to use PPP, you must configure the kernel to include PPP support (PPP requires BOTH pppd AND kernel support for PPP).
PPP (point-to-point) support (CONFIG_PPP) [n] y
Answer the other make config questions according to the hardware in your PC and the features of the Linux operating system you want. Then continue to follow the README to compile and install your new kernel.
The 1.2.13 kernel creates only 4 PPP devices. For multi- port serial cards, you will need to edit the kernel PPP sources to obtain more ports. (See the README.linux file that comes as part of the PPP-2.1.2 distribution for full details of the simple edits you need to make).
Note: the 1.2.13 configuration dialogue does NOT allow you to go backwards - so if you make a mistake in answering one of the questions in the make config dialogue, exit by typing CTRL C and start again.