Form 1040 is the US Individual Income Tax Return, the form that you use to calculate your tax liability and determine whether you owe tax to the IRS or whether you are due a refund.
Form W-2 is issued to individuals by US employers, to report annual earnings, taxes withheld, and other tax-related information. This is a form you receive; you would not prepare and file one unless you are also an employer.
Since you are living and working overseas, you would not be expected to have a Form W-2, but you must still file a Form 1040.
