When a person struggles with making a decision, it is called an internal conflict, as it takes place inside him. He may struggle between two options or in deciding the correct course of action. For instance, in William Shakespeare's "Hamlet," the titular character struggles to decide whether or not to revenge his father's murder by killing his uncle. The problem takes place within his own head.
The most common type of external conflict is when tension exists between two characters. They may be directly fighting against each other, or may be opponents competing for the same goal. A single piece of literature may contain various types of conflicts; "Hamlet" also contains an external person vs. person conflict between Hamlet and his uncle Polonius, who killed his father.
Characters may also struggle with the laws and social expectations of their society. In George Orwell's novel "1984," Winston Smith fights the oppressive laws of his society. Apart from struggling against laws and regulations, this type of conflict also includes a tension between the character and standard social customs and practices. If a character does not fit the social norms of his culture, he also has a conflict with society.
A character may find herself fighting against an element of nature, which includes a struggle against an animal or against the elements. Characters may be at odds with extreme weather conditions or may be fending off wild animals. Herman Melville's "Moby Dick" presents such a conflict, as Captain Ahab struggles to kill the whale that amputated his leg, Moby Dick.
This conflict can also include tension with a god or a supernatural being. It describes the struggle of a character against nonhuman and non-natural sources. A character may be struggling against her destiny, or in mythology, may have an issue with a god. An example can be found in Sophocles' play "Oedipus Rex." Oedipus receives a prediction that he will kill his father and marry his mother. He then struggles against his destiny and tries to avoid this outcome.