In Project, is it possible to add a new section in the "General" tab, below the already existing "Description"?
Everything I tried, creates a new section under the tab "Detail".
Thanks in advance,
Silvia
Yes it is possible. Thanks to the plugin Screen customization that you will find on our store.
The manual for this plugin is provided with it and will help you build your new fields in your new sections.
Thank you very much for your anwer but I think I didn't explain the problem correctly. We are already using the plugin "Screen Customisation" and I'm able to create new fields, new sections...my problem is that I'm not able to put the new section in the tab "Description" as shown in the image below.
I tried in different way, but the new section goes always under the tab Details.
Thank you very much for your help!
indeed I had misunderstood. 
So, yes, it's normal. The plugin is not intended to add sections at the tab level. The new section will be automatically placed in the detail tab.
A ticket is registered to add this feature to the plugin. Feel free to sponsor it! 