How to start the game on this??

Well... You go to your account using menu under your nickname at the top of the page. You download an installer, install the game, and then you run it. Or, you download a Galaxy installer, you install the Galaxy (a client, like Steam), you download a game using Galaxy and start it from there.

Would you care to provide more information, otherwise nobody will be able to help.

I love Sundays in here! :D

Im using Mac i download and install gogcom and i download a game when i go to my profile i can see i have 4 games and i play 0 min but dont know how to start the game...

If you mean you installed galaxy, click a game in the library. It will show ip on the left bar where you can click it and press play.

yes i install galaxy and i did find it in my library found 4 games but it show not complete so i clic instal but it do nothing just spinning how long it takes to install this?

Well, what is this, in question?

I'm getting this strange feeling that you're probably not old enough to be on this website.

Nope i Think im too old....
ok i download game on win but im runing on mac can i run this game?

Goto your account on the website. Find the game in your library:
https://www.gog.com/account
Click on the classic installers which you will find lower down the page. This will list at least 1 file, and most likely several. Click on each and download them (save to downloads). Once all have finished, double click on the exe to start install. Install to a folder not windows (I.e not program files), e.g c:/mygames. Now double click on the short cut on your desktop.
It's the files you downloaded you can copy to cd or disc and keep for any future needs, this is the big and only benefit of buying here.

YouTube videos to maybe help you.

GoG DOS games on Mac

Searching 'GoG on Mac' may provide other useful video how-to's. :)