Second person is written in the second person. "You".
Limited is limited to one character. Omniscient is... omniscient.
Not much fiction is written in second person POV, but an example would be Jay McInerney's
Bright Lights, Big City. Most people, me included, find that kind of narration precious and gimmicky and, well, just plain unreadable after about five pages:
"You wake up and take a shower. Your eyes are red and puffy, and your head feels like it's about to explode. You never should have mixed that good Talisker with Red Bull last night."
etc.
Third person limited POV is told through the camera lens of a single character (or only one character at a time, shifting to other characters perhaps, in separate scenes or chapters). But it is told using "he did X" rather than the first person "I did X". It is a very common narrative technique in modern writing. The key thing to remember is that, in using third-person limited, you can't present anything the narrative character doesn't or can't experience. You can't present other people's thoughts, or describe some happening outside the narrative character's sphere of observation.
Third person omniscient POV is likewise a "he did X" form, but narrated as though the author is a God-like observer, and pretty much anything can be included in the narrative, thoughts of many characters, descriptions of almost anything, etc. It was the standard fictional narrative technique of the 19th Century, and is still being used pretty widely today. It has a lot of tempting pitfalls for the inexperienced writer, however.
That help any?
caw