The main websitesource of info about W9 forms is

Here, you will be able to download and then you can print a W-9 form for free.
This four paged form entitled IRS W-9 is a request for a "Taxpayer Identification number and certification".
Pages 2, 3 and 4 are the instruction pages. It is a rather quick W9 form to fill out for most people.

They ask for your TIN or Taxpayer Identification Number.
This is the number that is either your Social Security Number as an individual or an Employer Identification Number.
For those who are requesting a W9 to be filled out, here are some instructions Instructions for the Requester of Form W9

If Spanish is your first language, you might be happier with the downloadable and printable Spanish version of the form W9.

Here is the W9S form for students or borrowers. It is a simple form.

Foreigners who are not resident aliens can download the W8 form for the similar use. You can use theInstructions for the W8Form.
Don't forget to get your form, and fill it out, for submission as time flies and you should be on time with this important tax prep info.