Inside caesar there are several .IMP files inside directory:

C:\Program Files (x86)\Intergraph CAS\CAESAR II 2016\Stoomwzn


where can i find a manual or a reading to understand the meaning of datas inside these files and what they are useful for?

I guess there are a sort of routines to generate input echo reports.

Yes, the .INP (not .IMP) files control the format of the input print format - Stoomwezen has some extra parameters to display.

thank you.
where can i find parameters list and an explanation to use them?

I know of no general list of the .INP content.
But by comparing the .INP content with the report display you will quickly see what is what.

The program formats the input echo based on the active .INP file in the \SYSTEM folder. Some reports offer several formats - for example, the ELEMENT list had ELEMENT.INP, ELEMENT0.INP, ELEMENT1.INP, etc. The program uses the file without the number in the name. If you wish to use a different "template" just copy one of those other ELEMENT files into ELEMENT.INP. (ELEMENT0.INP is a duplicate of the shipped ELEMENT.INP.) You can build your own templates.

Again, Stoomwezen has a special report to display its unique data.

Just to follow from Dave.
The most important word in Dave's post is "copy".
Keep a copy of all original inp files out of the box.
Keep a copy of any inp file that works before you edit it.
Editing an inp file is very easy by just following similar usage elsewhere in the file. e.g. Changing decimal places.
However, if you make a mistake, the system just stops. There are no error messages and no indication of what mistakes you have made. This is not a problem but you need to have a working copy that can be reinstated.
Edit and test in small baby steps in case you need to go back to a previous copy.