API's and more

I am trying to learn what everything is and how to go about starting a mashup. I wasn't sure what an API was, and that is what every site talks about with mashups. I took around 2 hours on May 23rd trying to figure out what an API is. API stands for Application programming interface. Wikipedia gives a full definiton, but basically it's and interface that is provided by a computer program to give functionality to that program. http://en.wikipedia.org/wiki/Application_programming_interface. Some API's require royalties for access, but those that don't are considered "open" and can be used for creating mashups. The programmableweb.com/howto site gives a step by step guide in creating a mashup. At this site you can also find a Database of API's to choose form according to what type of a mashup is being created. I'm still figuring this all out, but I also found on this web site how to sign up for an API. One example is the Google sign-up page. I will try these sites, figure out more what type of a mashup we are going to make, and what API we need to use.
Gina