In general, martial law is when military government employs in the suspension of ordinary law. Usually, civilian forces (like the police) make sure there is law and order. People are typically tried by a civilian judge but under martial law, the military restore order and implement laws, instead.
Martial law is control of an area by soldiers, not the police, different from military law.
Martial law is an extreme and rare measure used to control society during war or periods of civil unrest or chaos. According to the Supreme Court, the term martial law carries no precise meaning (Duncan v. Kahanamoku, 327 U.S. 304, 66 S. Ct. 606, 90 L. Ed. 688 ). However, most declarations of martial law have some common features. Generally, the institution of martial law contemplates some use of military force. To a varying extent, depending on the martial law order, government military personnel have the authority to make and enforce civil and criminal laws.