diff --git a/doc/how_to_write_an_exercise.rst b/doc/how_to_write_an_exercise.rst
index 06706cd..608d07e 100644
--- a/doc/how_to_write_an_exercise.rst
+++ b/doc/how_to_write_an_exercise.rst
@@ -5,11 +5,21 @@ To write a java exercise, the first file you need is config.json at the root of
 
 This file must have the following fields :
 
-- ``'customscript': nameScript`` in order to use an additionnal correction script (to check if Math is import for example). if there are no additionnal script, you still need to have this information.
+- ``'customscript': nameScript`` in order to use an additionnal correction script (to check if Math is imported for example).
+     If there are no additionnal script needed (nothing else than the test to check), you should set it to custom.sh else the code will not work.
 	
-- ``'execcustom': 0 or 1`` in order to indicate if the additionnal script should be executed (1) or not (0).if there are no additionnal script, you still need to have this information.
+- ``'execcustom': 0 or 1`` in order to indicate if the additionnal script should be executed (1) or not (0).
+     If there are no additionnal script, you should set it to 0.
+     If set to 1, the program that runs before the tests will execute the script.
+     If an error occurs in the custom script, the error message will be displayed but your script needs to set the message itself with::
+
+     feedback -i id_question -r failed -f "Your error message"
+     exit(1)
 	
-- ``'nexercices'`` which represents the number of exercices in a single task.
+- ``'nexercices'`` which represents the number of exercices in a single task. This will be helpful to indicate which question does not work in a single task.
+    In case of failure, the program that launches the tests will look for the one who failed and set the error message of the test as the global feedback message.
+    If you don't put the right number, it will still show the error message but it will be displayed in a code box with an additional sentence saying that "the code did not work"
+    rather than having just the error message displayed in the case you did put the right number of exercises.
 
 Here is an example of the file ::
 
@@ -78,6 +88,11 @@ Here is an example of the 'Tests.java'::
         }
     }
 
+Lastly, we need a 'student' folder with files called 'MessagesBundle_en.properties' for example which will hold the translations of the feedback.
+Each line should have the original feedback and the translated feedback.
+
+An example of line is : ``Impossible\ de\ d\u00e9coder\ le\ config.json=Unable to decode config.json``
+
 Lastly, we need a 'student' folder with files called 'MessagesBundle_en.properties' for example which will hold the translations of the feedback. Each line should have the original feedback and the translated feedback.
 
 Here is the structure you should have ::
@@ -93,3 +108,19 @@ Here is the structure you should have ::
 	└── Templates
 	    └── Student.tmpl
 
+Environment
+-----------
+
+In the environment tab of the task, you should select Docker as the environment type if you plan to do a coding question.
+
+If that is the case you should then select java8judge as the environment which is a special container with different global files useful for exercises (the program to launch the tests for example).
+Those files will be used in your exercise, thus you do not need to think about those files.
+
+You must also precise the timeout limit and the memory limit in case of a 'malicious code' from a student. The other parameters are optional.
+
+
+Subproblem
+----------
+
+You should enter a problem id and the problem type (code). Once you added this, you must enter a name for the question (Average xith 3 numbers for example),
+a context to precise a specific detail, the language and then you can save the changes.