Tamil and English are both spoken here. Some schools in Chennai teach their classes in English, and others are taught in Tamil. This is called the medium of the school. For example, an English medium school would teach all their classes in English. Around 57% of students in Tamil Nadu (the state that the city Chennai is in) go to English medium schools. Most of the remaining students go to Tamil medium schools. This is why a lot of people in Chennai can speak both Tamil and English.
A lot of the laborers in Chennai, such as waiters and cab drivers, are immigrants from other states in India. There are also immigrants from South Korea in my area of Chennai who mostly immigrated to India to work in the car companies. So apart from English and Tamil, some people speak Hindi, Korean and Malyalam.
The currency in Chennai is rupees. Currently, around 86 rupees is 1 US dollar.
A bottle of water costs 20 rupees, or around 23 cents.
