Reading scientific articles is a skill that you develop. Unlike a book chapter or magazine article you might read from start to finish, scientific journal articles (particularly research articles) are organized in a way that facilitates a more selective reading process, i.e. skimming and/or reading sections in a different order.
There is no single way to correctly read a scientific article. Even the researchers you're working with (PI, postdocs, grad students) may their own way of breaking down and reading articles, both within and outside of their field. Along with asking about their practices, here are some other resources: