This page is OLD. From about 2011. And it is done using an old KiCad. If you haven't already seen the "modern" (Feb 2017/ KiCad 4-0-4) versions of my attempts to help you master creating custom schematic symbols and footprints, work through that first.
Having said that, here's the old material, lightly tweaked…
I have created a separate page discussing the issues of establishing homes for the different files connected with your work (That has been updated to create a 2/17 (KiCad 4-0-4) version).
This page has been checked to see that confusion in my brain (before 9 November, 2011) about the roles of pin names and pin and pad numbers hasn't led to errors here. I have a page with more on this if you are really curious.
And there's another page… with some overlap of content, I fear, with further discussion of the management of .lib and .mod files.
Before you start this page
If you have not already been through my page about creating a footprint of your own, you might want to do that now. I have tried, really to be more concise in what follows, because if you have already mastered creating new footprints, you will find that creating (or tweaking) your own schematic symbols is a similar process.
A simple schematic symbol (aka "component")
Making the schematic symbol isn't terribly hard. Just be sure that you are using the word "component" in the narrow sense used by KiCad and me. In many places, I have moved on to a term I like better, "schematic symbol" (less ambiguous. KiCad is using it… and "symbol"… too… but not widely enough yet!)
If you haven't come here from the KiCadHowTo homepage, unless you are a KiCad wizard, there are things there which might help you get traction quickly.
You need schematic symbols right at the beginning of the design cycle, while you are using eeSchema to create the schematic. Happily, if you need a new schematic symbol, you can go to the component design tool directly from eeSchema… but first you have to set some things up.
Just once, "in the beginning", and once and for all, on a given machine, you should create certain folders, before you do the next thing. (Keep reading!). Setting those up is covered in my pages of 2/17 (KiCad 4-0-4) on the subject of custom schematic symbols and footprints. Go to the main tutorials menu page to see what's available.
Once in a while on a given machine, before you make your first "by you" schematic symbol, you should create a .lib file, to hold components made by you, and components "made" by you by cloning an existing component and tweaking it. You may want to make more than one .lib file, but you do not need one for each component you make or adapt. (Keep reading!)
Getting that .lib file created, and in the right place is covered in the new (2/17) tutorials.
So! We'll assume that you've set up the folder. And in the course of that, put a "starter" schematic symbol in your first .lib file. (Once ou have another schematic symbol in the library, you can delete the "starter" schematic symbol, if it wasn't useful for anything else.)
Note that creating a components library, is distinct from telling a given project to include that library in what it does. That is a second step, which is also covered in the new tutorials.
The next part of the story of creating your own schematic symbols is in the page that link will take you to.