Most of them would have seen a ever-standing long queue near Gemini Bridge in Chennai. You can see the location of U.S.Consulate through this map http://goo.gl/4t4Z2 . There are different kind of Visa(s) that you can apply to reach U.S.
For quick reference, please refer to the below F.A.Qs
Why do I need Visa?
Most foreign countries require approved Visas for the people from other countries to visit their country. The norms vary from country to country. This U.S. Consulate is responsible for issuing Visas for people visiting "The United States of America" only.
Can I apply for any Visa here?
The Visa interview happens here. For application and other such details refer to http://www.ustraveldocs.com/in/index.html . The visa interview for all the type of Visa for U.S. happens here.
The usual schedule now is to record your finger-prints in OFC and visa interview in the U.S. consulate on the next day. I had the OFC (offsite Facilitation Center) appointment scheduled on 30th May and U.S. Visa appointment on 31st May.
My appointment was at 8 AM for the OFC. I went there by 7.45 am. There was already a big queue in front of the OFC office. I looked for the parking inside the building. I went to the watchman near the gate and asked where to park my vehicle. He told "You can't park the vehicle inside. No Parking inside the campus". I had to park it out. I stood near the line and went into the Centre exactly at 8.00 AM. Only people who had appointment at 8AM were allowed in. I had to keep my bag with important documents outside the center and only plastic bags were allowed inside the gate! This OFC is specifically to get the fingerprints and photo. They don't ask any questions here and this is just a formality. This appointment is one day before the U.S. Visa Consulate's appointment. So, people coming from other states has to be in town for at least two days for the Visa interview.
For the U.S. Visa Consulate, my appointment was at 7.30 am. Again, this was the first available slot for the day. I reached the place by 6 am. I had to park my vehicle about 1 km from the Consulate and walk back. There is no place nearby to park the vehicle. I reached the consulate at 6.20 am. The queue was already long. It seems people were standing from 4.30 am! The place at which you stand hardly matters though. They started to verify the documents by 7 am and sent one-by-one in the queue. I know that the mobile phones and bags are not allowed in the consulate through by previous day's experience. So, I kept my bag and mobile phones inside my vehicle itself. To my surprise, they didn't even allow remote keys. Also, CDs were not allowed in. There was a small petty shop nearby and it did the safe-keeping job for the visa aspirants. They would charge Rs. 10/-. The receipt would also be provided and they give you a token. Then, You will be provided a number and the documents would be screened. After the screening, they check your fingerprints back for matching and ask you to proceed into the adjacent building. The officers arrive only by 8AM. Then each officer will take one-by-one in their queue. Keep an eye on your number and any of the TV screens. Easily you can see the counter number and stand in queue for your turn. The Visa officer will be inside a bullet-proof glass cabin and ask you few questions. This will be mostly related to who are you, Where you want to go, purpose of visit, how much time you will go etc.,
Then, if you want the courier to reach your office/home, you can give Rs.300/- and place the order. I didn't opt for this and I collected the passport directly from the Blue Dart Courier office. When you are collecting the passport, make sure you go with your original document and you have to sign in the copy as well for the proof.
All the best for your interview. Add your experience and questions in the comments below.