What are the different Source of Component Library (Sch / PCB)?

Component library creation and maintenance is considered to be one the most challenging part in Electronic PCB Design.

Should we make schematic symbols and PCB footprints from scratch or are there any places where we can find them available, ready to use?

Here is a list of place where you can find Schematic & PCB libraries:

Many a times a library is available in a different format, here is a list of tools you can use to convert to a desired format:

If you know any other useful sites, let me know, I will add them here.