When you apply for a loan or credit card, the lender makes an inquiry about your credit history to determine your repayment capability. It stays on your credit report for 2 (two) years and such background checks can lead to a drop in your credit score.
You can get your free credit report by visiting the official websites of the credit bureaus in India. Most of them offer one free credit report every 12 months. Many financial institutions, NBFCs, and aggregators also provide this service on their websites.
Having no credit score simply means that the respective person has never held a credit account so far. It is very common among young adults who are still in college.