i have got a simple question, but i want to be sure:
when i have in the themes folder an theme wich have this folders: "css", "images", "templates", for what i need this three folders in the folder my_site? can i delete this tree folders from Folder "my_site"? or how it works together?
Yep well those 3 folders are from back in the day when SilverStripe did not support themes so sites where all developed in the mysite folder. Now its recommended to make you template and css files as individual themes in the themes/ folder