After you get your visa and get to India you have to register with the police as a foreigner residing in the country. This is really common if you're staying anywhere as an ex-pat for any period of time. Sometimes it's as simple as filling out a form and having someone stamp it or a quick visit to your local constabulary.
In India I was given a guide (a godsend really) from HR at the company in addition to a driver and we headed off on a Saturday morning to the main police station in South Mumbai which houses the FRRO, Foreign Regional Registration Office. I was given this big folder of paperwork, mostly the same stuff I needed for the visa in the US. I also need my passport/visa and four more passport pictures and money to pay the fees. People were not at all certain what the fees would be. Anywhere up to 2000 rupees was estimated. It ended up being just 150 rupees, which surprised the HR guy. When I got to the entry to the FRRO the people at the desk reviewed my papers and then wrote some numbers on the cover and said I needed to watch for the counter inside. They then sent me through a door that my guide said was for foreigners only and so he could not follow. He said I would find a computer and I should enter my information.
There was a big room filled with folding chairs and lots of people from all over. There were computers in the back. I sat down at one and answered all the questions, Passport number, visa number, type, where issued, airline I flew in on, DoB, parents home, where I'm staying, airspeed of fully laden swallow, etc. I then needed to print it out. After asking, "What next?" I was pointed to the front of the room where there was an LED sign displaying counter numbers and which number was being served.
I found out that not everything is covered by this system. It turned out I was scheduled for Counter 3A, which was not on the board and was turned away from Counter 3 when it hit my number. I was told to wait for someone to come get me, which eventually did happen.
I had to go in and review the paperwork again, then wait, then pay the fees, then fill out a booklet with the same information on the printout that I had given them earlier. I guess they didn't save that data. Maybe that's good. Anyway it was typical duplication of effort.
Then I had to wait again.
Then they came out and handed me the book, now stamped and certified and said I was done and could leave. The HR guy was thrilled. It took 2 1/2 hours (mostly waiting) and we were done at 1230pm. He thought it would be at least 4pm before we got done.
So now I have my little black book that identifies me as a legal foreign resident of India. Apparently this is an important document in some circumstances which I hope not to find myself in. Or maybe I just need it to ride the train. Possibly I can wave it at shopkeepers who charge me the Tourist Rate and get the local price instead. Haven't had to try that yet. As I said, patience was the key, and having your paperwork sorted made it go twice as fast as usual apparently. Kudos to the people at my company in India for making sure it was together.