I am planning to visit the US for tourism. Until now I have never been to any foreign country.
I want to know whether the visa is issued for a stay in a particular city or whether I can travel to any part of the country?
They're for the whole country. There are no controls on the movement of people within the US, except for the usual requirements to show ID to get on a plane. In particular, if you drive across a state border, you will typically see absolutely nothing except a sign saying what state you're in now. A few states, such as California, have agricultural inspection stations near the border but these are designed to prevent the free movement of agricultural pests, not people. There are also some interior border patrol checkpoints, which are on highways around 50 miles from the Mexican border and designed to prevent illegal immigration and smuggling. You'd be required to show your papers there but, as long as you're legally in the country, you're free to pass through.
Since Alaska and Hawaii are disconnected from the other 48 states, there are some small differences with them. Getting to Alaska overland requires going through Canada so isn't travel purely within the US, even though it's travel from one part of the US to another. To do that overland, you'd need to leave the US and then re-enter; flying to Alaska doesn't count as leaving the US, even though you'd fly over Canada from most places. There are also differences if you travel by private boat or private plane but I'm assuming you won't be doing that.
(It would be nice to back up this answer with a link to some sort of official advice but I've no idea where to look for that, since it seems unlikely that there are lists of all the things that aren't required. You don't have to drive a red car, you don't have to carry an umbrella, etc.)