Open your Gmail account on the webpage, select Contacts in the upper left, click More/Export..., select vCard format, Export, and save the contacts.vcf file.

In TB (or Address Book), Tools/Import...Address Books...vCard file...select the contacts.vcf file. You may have to close and reopen Address Book for the new contacts address book to show its contents.

I have the file in my documents but it doesn't import to my Thunderbird address file.

When you import contacts.vcf as described above, a new address book named "contacts" is created in Address Book. The contacts in "contacts" can be copied to Personal Address Book (or any other address book) by drag and drop. Make sure View/Layout/Directory Pane is checked in Address Book.