Hi there I am using a Mac. Will these GOG games work?

NO. You need to use Parallels, Boot Camp, or some other virtualization software to play GOG games on a Mac.

Officially, they are not supported. Only WinXP and Vista.
You may have luck with the SCUMM games (and possibly dosbox), but you will need to get the OSX versions from their website (as the installer only includes the win version) and import the files manually. GOG will not support them, but some community members that use this setting may be able to help.

On the bright side, all reports say the WEBSITE works a treat on a mac!
This is the list of games that will work under linux & WINE, there's probably good info in there for macs as well

Thread already exists.
Other than that remark, you'll need Darwine, at least to install the games, then you have a few options:
1. Run the game through Darwine, using the windows binaries (should work with most games, including the next two cases - double-click the .exe, which probably sits in /Users/<you>/.wine/c_drive/Program Files/GOG.com/<game> ... a tip, make an alias to the GOG.com folder somwehere you can more easily find it, the .wine folder is hidden, so you won't see it in the Finder).
2. If the game runs through DOSbox, feed the game folder to Boxer, to create an easily-run package of the game.
3. If the game runs through ScummVM, use its mac version to find and run the game, instead of the Windows version that is installed together with the game.