Detail on how to earn money legally through internet? Are ptc sites helpful?

Either have or acquire a marketable skill for which people are willing to pay you for.

For example, I have a friend who has an engineering degree and after serving as a missionary in Japan for several years, he is fluent in that language. He translates technical manuals regarding farm equipment from English to Japanese and visa versa.

He works from home, entirely online. His specialty is grain elevators.

There is nothing.

To earn money online, you need to have a product or service that other people would pay for.