You can always think of the narrator as a person with opinions, views, and a specific way how they think and talk, that is, their voice. Therefore, when a narrator narrates a narrative, the real events are "filtered" through the viewpoint and voice of the narrator: we get the narrator's interpretation of the events, and we are told the story in his or her words.
You can think of it like this:
Your friend Robert tells you how he and his team won the soccer game yesterday. Since Robert tells you the story, he will tell the events from his viewpoint: how he experienced it, what he did and said and thought, what it means to him, and so on. He may supplement his narration with what others have told him.
When Robert tells you of the soccer game he played, Robert is both the protagonist and the first person narrator of the story ("I took the ball and..."). We see the events through his eyes and are told the story in his words. The events are "filtered" through the narrator Robert. Another participant or an outside observer would have told the events in another way.
After talking to Robert you meet your friend Olivia and tell her what Robert told you. But you will very likely not repeat what Robert told you word by word, rather you will tell the story in your own words.
When you tell Robert's story, Robert will remain the protagonist, but you will become the third person narrator of Robert's story ("Robert took the ball and..."). Since you aren't omniscient and don't know everything that transpired, your story will be third person limited narration. And since, in the telling, you will interpret the events and tell it in your own words, the story will be "filtered" through you.
Maybe you get curious and you ask everyone who was at the game what happened and how they experienced it and you weave a story from that. You'll then be an omniscient narrator, because you now know everything that happened and everything that anyone thought.
I think the difference between "subjective" and "objective" omniscient narration is explained well in the text you link and I don't need to repeat it.
Generally, narrators differ in what they know (omniscient versus limited), the viewpoint (first or third person), their interiority (what your text calls objective versus subjective, that is, does the narrator recount the thoughts and emotions of a character or just describe what can be observed from outside of that character), their trustworthiness (does the narrator tell the truth or lie), and so on and so forth.
Personally, I find all these attempts at categorizing and naming certain narration styles incomplete and limited. None of them manage to describe all the fine nuances that exist between different narrators. My recommendation is that you forget about these terms (e.g. "subjective omniscient narrator") and think about what narrative style best fits your story.
