Hello and Welcome to Openstreetmap :)

My french is rather basic so please let me use English:

The OSM-community has written quite some documentation in a wiki which you can find here: wiki.osm.org
As a beginner, you might wish to start with these pages (change the language at the top of the page)
https://wiki.openstreetmap.org/wiki/DE:Beginners%27_guide
https://wiki.openstreetmap.org/wiki/DE:How_to_map_a

Should you have questions (which most users have most of the time, don't worry) you might want to check out any of the chatrooms mentioned here
https://wiki.openstreetmap.org/wiki/Contact_channels#Chats.2Fmessengers
There should also be some places where people speak French :)

Happy Mapping
silversurfer83