This is best illustrated by an example. Suppose we have three candidates, A, B and C, and that there are three voters with preferences as follows (candidates being listed in decreasing order of preference):
The majority view of the voters in this situation is that B is better than C, who is better than A, who is better than B, who is better than C, etc.
See also: [Arrow's Impossibility Theorem]?, Paradox, Condorcets Method.