Great question and very relevant today as there are a lot of different factors that go into your credit score that you wouldn't know (many adults don't even know). Yvonne is right that a secured credit card is one way to start building your credit score. If you have a parent that is willing and able, having them cosign on a loan (car loan or apartment lease agreement for example), or credit card is another way to start building your credit. There are several credit cards/accounts that are intended to build a young person's credit - you would be an authorized cardholder with a limited spending amount. As soon as you have at least 6 months of credit history under your belt, you will qualify for other forms of credit, but definitely start small and only what you're able to pay in full. Don't be fooled into paying only the "Minimum Amount Due," as that will lead to a lot of fees and interest. Slow and steady will win the race! I like the website NerdWallet for straightforward credit advice, and here's a good article for you:
It is never too soon to start building your credit history - in today's world of PayPal and Venmo, there are limited ways to build your credit score, to the point where those in the industry are even questioning the utility of credit scores to determine if someone can pay on their loans. You will be ahead of the game if you start now by instilling some discipline in the way that you spend. Good luck!