Citadel Deathworld Forest Base paint is designed to give a smooth, solid olive green color over a substrate and for that reason this will almost always be the first paint you use on a miniature. Shake the olive green paint before using (you can make this easier by adding an agitator ball).
The olive green paint can be a bit thick sometimes and then you just add a few drops of water on 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 olive green 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 Deathworld Forest base paint.
The color of Citadel Deathworld Forest (21-15) is similar to: The Army Painter Venom Wyrm (WP1461); Old Citadel Gretchin Green; Vallejo Game Color Heavy Khaki (72149); Vallejo Model Color Russian Uniform WW2 (70924); Instar Savannah Green; Reaper Master Worn Olive (9159).