There are two main types of conflict: Internal Conflict and External Conflict. Internal conflict, or man verses self, is a conflict where a person is fighting with their own morals or feelings. For example, a person is on a diet and knows that a huge piece of chocolate cake would be bad. The conflict which arises within the person (one side wanting the cake and the other not wanting the cake) is an example of internal conflict.
External conflict, on the other hand, is very different. External conflict is comprised of three subcategories: man verses man, man verses nature and man verses supernatural.
In man verses man, two people are in conflict with each other. Sometimes, the people simply do not like each other. Other times, the two people see the other as an honest threat.
Man verses nature is a conflict which is brought a brought about when a human clashes with nature (a person in a storm trying to survive or even Katniss during the Games trying to fight through the woods). Man verses supernatural exists when spirits or ghosts conflict with a person (for example, in Twilight or Harry Potter).
Therefore, the conflict between Katniss and President Snow is one of an external nature given it sets one person against another (Katniss against Snow).