Strokes can be caused either by blockage or rupture of an artery
Ischemic strokes are produced by arterial blockage. 
The resulting inadequate blood flow (ischemia) deprives the brain of oxygen and glucose and slows the removal of metabolic wastes.  The parts of the brain that the occluded artery can no longer adequately supply begin to function abnormally or cease to function.  If ischemia persists, brain cells die and then swell. The term "infarct" is commonly used to describe such a region of dead tissue.  The brain is at special risk for ischemia because there is not enough redundancy in the arterial supply to maintain adequate blood flow if one artery is suddenly occluded.
About 80% of all strokes are the ischemic type.

A Transient Ischemic Attack (TIA) is the result of a brief, transient episode of focal brain or retinal ischemia. Neurological deficits suddenly occur and then, unlike a stroke, disappear completely.  Most TIAs last less than an hour. In fact, in the vast majority of cases, the patient experiences symptoms for less than 10 minutes. However, the standard current definition includes events that persist up to 24 hours before they fade.  Unlike a stroke, no neurological deficits remain once the attack has ended because no brain tissue is permanently damaged.
A TIA sounds the alarm that an ischemic stroke may be imminent.

Hemorrhagic strokes are produced by arterial rupture
Depending on the vessels involved, bleeding can occur within the brain and its ventricles or around the brain in the subarachnoid space.  The blood produces injury by distorting, compressing, and tearing the surrounding brain tissue (including its blood vessels) or by increasing intracranial pressure.
About 20% of all strokes are the hemorrhagic type.