Here is an example of a piece I did and once you hit it with 2 coats of matte. You will never see the gloss.
Look at the bottom of the tank's side near the tread. You will see where it pooled in the corners slightly to give a dirty look. The camo here was all airbrushed so a wash with very light pigmentation is the right tool. It also fills the joints between plates and rivets.
Note the areas between his glove and the sleeve of his coat. That is not black lined it is the wash settling in.
If you take note of the leather on the sides of the turret. You can see the highs and lows of the bag.
Experiment with washes. Remember you dont have to use it straight out of its container. Try thinning it out on your brush with some water. See what that does. I think I might have made more containers of different color washes than I care to list. The best way to learn is to do. Get some junky minis you dont care about and play around with it.
Here is a definition I found in the Painters Dictionary which helped me out when I first started using washes.
A wash is a thin layer of ink or watered down paint (usually a darker shade of the colour being washed over) that runs into the recesses of the miniature creating shadows.