The fastest way to earn bitcoin is the same as the fastest way to earn any form of currency - work for it. If you have a service you can offer online, such as programming/coding, web or software development, writing, marketing, etc. then you might be able to sell your services for bitcoin. If you have a product you can offer for sale, then you can sell it for bitcoin. However, by far the quickest way for you to earn bitcoin is going to be to buy some with fiat. If you have a job, great. If not, getting a job and using your income to buy bitcoin will be much faster and earn you much more than almost any other option as a newbie.
Thank you for the advice, I meant to earn BTC online, not by investing hard-earned money
I have been searching for websites paying in crypto, like freelancers website. I am bombarded in Facebook with ads that promise to earn money using apps, but I can say they are probably scam.
I guess I need to do a better research.