Third person limited point of view is a method of storytelling in which the narrator knows only the thoughts and feelings of a single character, while other characters are presented only externally. Third person limited grants a writer more freedom than first person, but less than third person omniscient.
For example, For Whom the Bell Tolls sticks firmly with one character's consciousness, that of Robert Jordan: "This Anselmo had been a good guide and he could travel wonderfully in the mountains. Robert Jordan could walk well enough himself and he knew from following him since before daylight that the old man could walk him to death. Robert Jordan trusted the man, Anselmo, so far, in everything except judgment. He had not yet had an opportunity to test his judgment, and, anyway, the judgment was his own responsibility."
The reader will only know Anselmo's thoughts and responses insofar as he reveals them through his actions. But Robert Jordan's thoughts will be shared throughout the story. It's his reactions and his interpretations of events that the reader will understand and follow.
Because third person limited is defined mostly by what it doesn't do, it may help at this point to read an example of third person omniscient for comparison.