Something especial is even greater or more than it usually is. The letters you get from your Japanese pen pal will be of especial interest to your brother, who collects foreign stamps.
You can use the adjective especial to emphasize the unusual or singular nature of something, or its importance. Doctors and nurses need to take especial care to wash their hands often, and it might give your grandmother especial joy to see all of her thirteen grandchildren pose for a photograph together. Especial is less common than its near-relation, special, and both words come from the Latin specialis, "particular."