Pratice well as Amazon, Microsoft do have online coding contest as part of their recruitment process.
For general working of the input/output statements for all different languages in this Hackerrank environment, check some of the examples here by choosing "Sample problem statements" from the following link https://www.hackerrank.com/environment .
Most important - Change your username to either "your name + your roll number" or "your name . your roll number" or "PSG.IT. your roll number" Example username - "sriram.10I349" or "PSG.IT.10I349" for easy validation.
You could change your username by clicking your name in the top right of the page and select "Profile" and choose "Edit profile" in the consecutive page, then modify your username.
Tips : 1). Use brute force approach till you pass 30-50% of test cases.
2). Do not care about the naming convention and the formatting of the code until you clear all the test cases.
3). Everytime you code some module of the problem, use ouptut statements such as cout or system.out.println() depending on the language youare using to check if you are in the right track.
4). After you solve all the test cases, it's time to look at the formatting and naming convention.
5). Use "compile and test" option in the environment to test it before submitting the solution.