In a nutshell, Steps 1 and 2 of the USMLE can be taken at various centers around the world, including India. Step 3 of the USMLE must be taken in the USA. Having completed Step 1 and 2, you can get a visa from the US embassy in India to visit the US for taking Step 3. You would need all the documentation for your intent and purpose, such as the proof of having completed Steps 1 and 2, and registration for Step 3. Additionally, you would have to provide proof of financial ability to sustain yourself while being in the US. If you have some friends and relatives in the US, they can prepare a letter offering you to stay with them during your visit to the US. This will reduce the demand for solid proof of your personal financial ability. Your intent for the visit must be that of a temporary stay, and NOT employment. Those are the rules, but reality is a bit different.

Once in the US, you can take Step 3 and then interview with various hospitals and medical practices. If a suitable match is found for Residency, the prospective employer will have to sponsor you for a temporary work visa, such as H1. Once you obtain H1 visa, it is fairly easy to have it converted to the permanent resident visa, more commonly known as the Green Card. However, it does take time, money, and patience. By the way, Residency pays around $30,000 per year, which is enough to sustain oneself.

As you may recognize, the process has inherent risks. You may not be able to find a residency and thus a sponsor for H1, in which case you must return to India. This could be a severe financial blow to an average individual.