How does decoder interface with galileo?

Hi, Im a little confuse about how does decoder interface with galileo. What pin i can use? What the coding i must used? And what the difference with encoder?

Thanks

Im a little confuse about how does decoder interface with galileo.

What decoder?

What pin i can use?

For what?

What the coding i must used?

What are the requirements?

And what the difference with encoder?

What is the difference between and encoder and what? An elephant?