Citadel Death Korps Drab Base paint is designed to give a smooth, solid green-grey color over an undercoat and for that reason this will almost always be the first paint you use on a miniature. Shake the green-grey paint before using (you can make this easier by adding an agitator ball).
The green-grey paint can sometimes be a bit thick and then you just add a few drops of water to your pallet. You really don't need a lot of water. Something to watch out for is to make sure you don't apply too much paint so that you don't start to hide details.
Another important functionality of this green-grey paint is that it not only covers the undercoat, but also covers other colors. So if you later miss something about this color, you can easily paint over it with this Death Korps Drab base paint.