At certain times, a model or unit might be called upon to take a Leadership test.
To take a Leadership test, roll 2D6. If the result is equal to or less than the model's Leadership value, then the test has been passed. If the result is greater than the model's Leadership value, the test is failed. This will normally involve the unit turning and fleeing from the enemy or some other negative outcome.
If a unit includes models with different Leadership values, always use the one with the highest Leadership. Note that a unit that has a LD of '0' or '-' automatically fail Leadership tests.