To make a folder private:
Change the folder's properties, giving yourself (the owner) read, write, and execute permission, but giving no permissions for group and other. This means that only you and the root user can view the contents of the folder.
To make an object that you've created available for everyone to use but protect it so it isn't inadvertently overwritten:
Change the file's properties, giving read and execute permission to owner, group, and other. Don't give anyone write permission.