update episode 4

Author: JaroCamphuijsen

_episodes/04-toy-example.md

@@ -5,12 +5,48 @@ exercises: 0
 questions:
 - "Key question (FIXME)"
 objectives:
-- "Excecute ESMValTool using the example recipe provided."
-- ""
+- "Explain how ESMValTool is structured."
+- "Execute ESMValTool using the example recipe and diagnostic script provided."
+- "Inspect the output that was created by running ESMValTool"
 keypoints:
-- "First key point. Brief Answer to questions. (FIXME)"
+- ""
+- "The recipe tells ESMValTool what parts of its core functionality it should run and on what 
+data."
+- "The diagnostic script is tailor made by the diagnostic developer where functionalities not 
+supported by ESMValTool can be implemented in the processing pipeline."
 ---
-Now we have installed and configures ESMValTool it is time to run a simple example and play with it. For this you need the data that you downloaded in the [setup](https://escience-academy.github.io/lesson-esmvaltool/setup.html).  
+Now we have installed and configured ESMValTool it is time to run a simple example and inspect 
+what it produces.
+
+For this we need our general ESMValTool settings from episode 3 (configuration), the example data 
+that you downloaded in the 
+[setup](https://escience-academy.github.io/lesson-esmvaltool/setup.html) and an example recipe to 
+tell ESMValTool what it should do. Let's make sure you have all set to continue. Check whether 
+you can find these three items in your ESMValTool folder.
+
+> ## Exercise
+>
+> Find all the 
+>
+{: .challenge}
+
+
+As already mentioned in the 
+[introduction](https://escience-academy.github.io/lesson-esmvaltool/01-introduction/index.html), 
+ESMValTool consists of two parts: the core and the diagnostics. The core part (also called 
+ESMValCore after its repository name) contains the code to run the actual software as well as 
+several preprocessing functions that are widely used. The diagnostics part (confusingly situated 
+in the repository called ESMValTool) mainly contains so called recipes and diagnostic scripts. 
+
+The recipes describe the analysis pipeline and tell ESMValTool which actions to perform on what 
+data. 
+
+
+
+~~~
+esmvaltool -c config-user.yml recipes/recipe_python.yml
+~~~
+{: .source}
 
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