Third person is when your narrator isn’t actually part of the story. This allows you to develop a much broader world. The reader can see what’s going on in multiple locations and through multiple viewpoints.
Within third person, there are multiple levels of POV, which determine how close you get to the character’s thoughts. Your options are omniscient, objective, limited multiple, and limited close.
Third person omniscient is when the narrator is basically God. The narrator can see everything that is happening and knows all the characters’ thoughts and feelings. Omniscient POV was very popular in classic literature, such as Dickens and Hardy, but has fallen out of popularity, primarily because a closer POV is more engaging to the reader.
Third person objective is when the narrator describes actions and events, but only tells about them objectively, and does not intrude upon the characters’ thoughts. This is even less engaging than omniscient because the reader never really knows what a character is thinking or feeling and therefore doesn’t empathize with the character nearly as deeply.
Third person limited POV is a little closer, limited to the thoughts, feelings, experiences of one character at a time. You can have multiple limited POVs within one story, but be careful to differentiate between them so the reader knows whose POV they’re experiencing at any given time.
Third person close is very similar to limited, as in it is limited to one character at a time, but it is so close it’s almost like first person, except it’s still “he/she” instead of “I”. Like limited, you can get into a close POV for more than one character, but be sure to be clear about whose mind you’re in and whose eyes you’re seeing through.
The preferred style for most modern storytelling is to use limited/close POVs. Like first person, this style draws the reader in and helps them to experience the story along with the character. So, unless otherwise specified, most of my advice will be given with the assumption that you’re going to be writing your story in either a limited/close or first-person POV.
Head Hopping is a term that is used when you switch POV characters mid-scene. If you’ve been in Helen’s POV, describing Troy and her trauma of being kidnapped, and then switch to the servant who is overwhelmed by her beauty without a scene break, you have hopped from Helen’s experience to the servant’s. This is confusing to your reader, because all of a sudden, instead of being Helen, they’re seeing Helen. It is a quick way to pull your reader out of the story and then you risk your reader losing interest. Stick with one POV character per scene, and if you must switch POVs in order to move to another location or reveal critical information that Helen can’t know, then have a scene or chapter break.