Here you will find links to interesting sites, but also a section on copyright.
Excel Made Easy: a nice tutorial on Excel by the same author.
Simple Excel: a tutorial on old version of Excel.
Si vous n'avez pas les droits sur l'information, dans ce cas il faut demander l'autorisation.
Be careful when you make a presentation for professional purpose or for the purpose of presenting to the public for commercial purposes, scientists, etc ... ask yourself the following questions:
The information I present is it public or private sector? Does this information belong to me or does it belong to someone else than me?
Do I have rights to the information (image, text, video, ...) I present?
If you do not have rights to the information, in this case you have to ask permission.
A basic explanation of the Wikipedia copyright (English)