Setting Up RAMPS

So, my RAMPS and drivers just arrived. The arduino is still in the mail. I have three questions about setting it up.

First: The RAMPS came with a through-hole component -- a diode, I think -- taped to the bottom, like a spare. What is this for?

Seconondly: I have DRV8825 drivers, which could fry my steppers if I let them. How do I tune them without doing that?

And thirdly: I feel stupid for asking this, but -- which way do the drivers go into the sockets?

You could look for images in google image search to see the direction of the stepper drivers.

The stepper drivers are calibrated with vRef, google that too, there is much tomfind about those subjects

According to the Geeetech Wiki (I have Geeetech drivers) the Vref pin is accessible through a "circled" uninsulated via, but for me it seems to just be tied to the positive power input. I also am not seeing any voltage across the trimpot, like it isn't being used. Any ideas?