Saving Components into a New Library
On the top toolbar, click the "Create new library and save current component into..." button:
A new library window should appear.
Name your library then navigate to the folder you want the new library to be saved in:
Now click "Save".
Changing your Default Component Library Folder for the Current Electronics Project
You need to do this for each new project you start. Each project should have its own library folder that contains all the libraries of components required for its schematic.
On the schematic editor window, click Preferences>Library
then click "Default Library File Path" then navigate to your custom library folder then "Open".
Now add and remove libraries from the list until you have just the libraries you need for the project. The libraries must all be contained within the default library folder that we set just before.
Note: if you wish to use the default kicad libraries, you will need to copy/paste the default kicad libraries from "/usr/share/kicad/library" to your default library folder for your project. You may need to enter the following command in Applications>Terminal to gain permission to copy/paste from your root folders.
On the library configuration window, click "Save Cfg" (configuration) then navigate to a folder of your choosing to save the KiCAD project file.
Now anytime you start KiCAD wanting to continue on an existing project, go File>Open then navigate to your project's .pro file then click Open.
Adding a New Component to an Existing Library
On the library editor window, rename your component by right-clicking the part name field then selecting "Field Edit":
The edit field window should appear. Change the value to another part name:
Now click "Ok".
On the top toolbar, click the "Select Working Library" button:
The select lib window should appear.
Select the new library you made and configured:
On the top toolbar, click "Save current loaded library on disk." This will save your new component into the library that you created before.