Admission requirements vary between universities and subjects in India. You will generally need a higher education entrance qualification. In addition, almost all universities take entrance exams. For further admission details you will either have to contact your desired university or take a look in a local newspaper, as they sometimes offer information on admission requirements as well.
Most foreigners in India do not have to take entrance tests but will receive preferential treatment. You will be accepted to a university only on the basis of your higher education entrance qualification. In return you are expected to contribute to a building fund and have to pay higher fees, which explains the special treatment.
The teaching language at most Indian universities is English. Especially in management, scientific and technical subjects you will only find English used in class. Some universities, however, have started offering their courses in local Indian languages as well, but only in addition to English.