H.G. Wells wrote The Island of Dr. Moreau in a first-person central narrator voice. Now that's a whole bunch of words, but grasping the meaning is pretty easy once you break it down. So let's do that with the following example:
I felt I had [Montgomery] at a disadvantage, had caught him in the mood of indiscretion; and, to tell the truth, I was not curious to learn what might have driven a young medical student out of London. (4.18)
We can tell this is first-person right away because the speaker refers to himself as "I." It's that simple: first person equals the "I" pronoun. Done and done. We can tell this is a central narrator because the events are happening to the person telling the story. The narrator is at the "center" of the action, and we also get information regarding his feelings and thoughts. In the case of the example, he isn't curious to learn Montgomery's secret and feels he has his friend at a disadvantage.
Well that wasn't so tough, was it?
The advantage to this style is that you get to experience everything with the narrator: his actions, fears, joys, and thoughts. Like him or not, you really get to know Prendick by the end of the novel.
A possible downside is that story cannot inhabit the view of Dr. Moreau or Montgomery, or better still one of the Beast Folk. This can be frustrating when Prendick doesn't receive information about those characters that we might want. In the example above, Prendick may not be curious why Montgomery had to beat feet out of London, but we might be. Come on, what did he do that was so bad that he could only find a home with Dr. Moreau?
We call this a Tootsie-Pop question, for the world may never know.