It would seem you are referring to editorial photography where you are producing images for various magazines either as a staff photographer or freelancer. The easy answer is editors are looking for published images that you have produced for your clients. Your website, or digital portfolio, should contain solid images that have a central theme to them. National Geographic is the prime example. The photographs are illustrations that help explain the written story. To get started, assign yourself assignments that require a series of photographs that explain the story you are telling. I suggest you look at the work of established editorial photographers to get a feel for their use of light and composition.
I wish you all the best in your journey.