Internal conflict can be defined as a struggle that comes within the mind of the character. This may be a decision that the character has to make as to what to do next, or whether they should befriend another character. In The Dark Knight, Batman choosing whether to rescue political celebrity Harvey Dent or his somewhat girlfriend Rachel from the Joker's trap is a typical example of an internal conflict.
External conflict is broken down into four categories: man vs. man, man vs. nature, man vs. society and man vs. force. Man vs. man is the most identifiable and easy to follow, so let's take a look at some other types of external conflict.
Man vs. Nature - A hunter trapped in the woods without shelter is an example of man vs. nature. He is up against the elements and struggling to survive exposed to the cold and danger of the woods.
Man vs. Society - Society can be defined in this sense as any group of like minded people. In Mean Girls (we've all seen it, just admit it) Cady has issues with the Plastics, a group of popular girls who dress, think, and talk alike. Cady up against the Plastics is an example of man vs. society.
Man vs. Force - Not often seen in literature, force is anything that can't be explained by science. A horror movie in which a teenager is trying escape a haunted doll is example of man vs. force.