I never play games on the computer but I found this game and thought it would be fun so I bought it and tried to download it but I can't download it without it being "damaged" and I have no idea why. Help would be much appreciated. Thanks.

I'm wondering whether that is a serious question... Anyway, if you refer to it downloading a DMG file (as in 'disc image') there shouldn't be a problem. Just double-click to open and drag the game wherever you like on your computer to copy it onto your HDD.

In case you're talking about a repeatedly corrupted download you may want to write GOG support about it since that may be a server issue.

Same thing happened to me... just finished downloading it earlier and received the message about the application being damaged. Contrary to what you might believe based on the message, it's apparently a security related issue caused by something called Gatekeeper for OSX.

The following steps fixed the issue for me:

Problem
Trying to launch the application for the first time, you get a message from OS X telling you that the app "is damaged and can't be opened".

Solution
OS X Gatekeeper shows this message because the application bundle is not digitally signed. To run the application for the first time, you will need to disable Gatekeeper as follows:
Go to System Preferences... | Security & Privacy | General tab.
Click the Lock icon in the lower left corner and enter your password to make changes.
Select Allow apps downloaded from: Anywhere.
You can enable Gatekeeper again after the first successful launch of the application.

https://wiki.almworks.com/pages/viewpage.action?pageId=15729485