As of October 3, 2013, this online form became mandatory for nonimmigrant visas (including K1, fiancee) at all U.S. consular posts worldwide.
To begin completing the DS-160, online, go to: https://ceac.state.gov/genniv/
You must first print out the "Application ID' after beginning the form, so that you can return to the form, after saving, to continue from where you left off.
While completing the form, you must upload a digital passport-style photo to the application.
After completing and "digitally signing" the form, you will need to print out a completion certification to take to your Embassy (or consulate) interview.
Also, go to:http://www.immihelp.com/visas/ds-160-form/
for an excellent description, with samples, of the DS-160 requirements.