After four decades in print, radio and television journalism, I am extremely familiar with the assigning, selling or licensing of rights to a publisher or broadcaster. But it would take me many pages of detailed explanation to even make a tiny dent in the topic. And after you’d bored yourself silly reading my long answer, you might feel you still don’t understand what it’s all about.
Frankly, I think it’s too early in your budding career as a freelancer to worry about rights. You must spend your energy, enthusiasm and brain cells on creating articles. Without articles to sell, the matter of rights doesn’t arise.
About one-third of my students worry unnecessarily about little details like rights, because they have “fear of writing” and want to worry about everything except getting on and creating articles.
For now, just create articles.