How to get a y value from terrain at a specific x,z coordinate?

Basically I have A drone game of sorts; a little drone model that you can fly around in a small worldspace. There is a terrain that I got from the asset store, and I want to be able to create an altimeter of sorts; something to tell the height of the drone relative to where it is over the terrain. So over a mountain, the readout would be lower than if the drone was at the same height over a valley. I'm pretty sure Terrain.SampleHeight() is what I need but if so, I have no clue how it works. Hopefully someone can help me out. Thanks!