What is the relationship between imports and exports in a mercantilist economic system?

Mercantilism consisted of lowering imports and increasing exports.

The system of mercantilism was developed mostly by the Dutch and carried on in their colonies, especially those in America.

Exports were goods that other countries needed, and so those needed to be increased.
Imports were goods that your country needed, and so those needed to be kept to a minimum. 
An entirely self-sustaining country could be achieved with a high export rate, which would increase their wealth, measured at that time in gold.