IELTS is a English test that you have to take to go abroad and study. It is a language proficiency test and not an entrance exam. So once you decide which country you want to go, you register for IELTS on their website and book your slot. There are test centres all over India and you can choose a test city and centre. Based on the slot, you write IELTS and get your score. Based upon the score you can apply for the Universities. Please check the website for the registration process.