Hello there! What version of the system are you running? Is it Ubuntu 16.04? :) As I understand, you run Ubuntu only from the DVD - it's called "a live system". DVD discs are read-only so you are definitely not able to save any files to the disc. You should be able to write files to your hard drive, though.

However, for full experience, I would recommend installing Ubuntu on a hard drive. Here's an official guide from the Ubuntu website: https://www.ubuntu.com/download/desktop/install-ubuntu-desktop

You have to be careful, so you won't erase your already existing data from the hard drive! If you are not sure how to do so, ask or hire someone more experienced to do that for you :)

If possible, please contact our support, here we will be able to help you in a best possible and more detailed way:
https://www.gog.com/support/contact

Ok, but are you aware that live sessions (system ran from DVD) are not persistent by default? That means you won't be able to save your game and be able to access the save file after you run Ubuntu from DVD again.

(Of course, there are workarounds for that, but I would really recommend you to install Linux on a hard drive, even an external one, if you want to play games on it).

In short, to install and run Darwinia on Ubuntu you should:
1. Download the GOG installer of the game (the file should have .sh extension)
2. Open the terminal in the folder where you downloaded the installer
3. Type:

chmod +x gog*.sh
./gog*.sh

4. A graphical installer should launch, follow the default steps to install the game.
5. Run the game by clicking the icon that should be created on your desktop (or the menu item accessible from Ubuntu dash).

That's the point - you don't have to. The shell will replace the asterisk with the remaining part of the filename!