Well, installing a driver from source is not as straightforward as installing a software. First you have to install the kernel sources (that is the development files of your currently running kernel). They are needed because drivers are kernel modules and the installation requires all those files related to the kernel which usually are not installed by default.
Installing kernel sources is as easy as opening your favorite package manager and look for them. Just be sure to install the sources matching exactly your kernel version.
Anyway, before proceeding I'd wonder if you really need to install the i915 driver from source. The intel graphic chipsets are well supported by linux and the i915 driver is usually loaded out of the box at the time of the system installation. You can check it by issuing the following command in a terminal:
Here is the result from the machine on which I'm typing, which uses the Intel Graphic Chipset embedded into the motherboard:
$ lsmod | grep i915
i915 28232 2
drm 74644 3 i915
The dollar sign in the above example is just the shell prompt (it helps to distinguish between the typed command and the resulting output below). As you can see I have the i915 driver already loaded and I had not to install anything from source. Hence my question: did you notice some problem in the graphic display? Or in other words: why do you need to install the graphic driver from source?