Spanish rapier fencing or sword fighting is slightly different from English or Italian swordplay from the same time period. This site by Richard Marsden has a basic introduction if you would like to see how it works. The overall system is called Destreza.

If you're not interested in that level of detail, simply put, the Spanish system is centered around the idea of a circle which surrounds each participant. That circle is defined by where you can move and where you can strike with your sword. If you move, your circle moves with you (this is something which seems to get lost in translation). You plan your action based on the circle. The circle is most important for what is called the curved step. There are also questions of blade control, distance, and timing, which differ in various ways from other countries.

I have also looked at Fiore's Armizare and have a certain measure of practice as well to aid in understanding how rapiers were used in combat.

Here I am at the New Jersey Renaissance Fair (2015) fencing against my wife. It was very silly but fun.