I'm new, I was wondering if my topic was available to do. I couldn't find an answer in any previous discussions. Any help would be awesome, thank you.

Kind of. You can start them using steam anyway .Under games in steam click "add a non-steam game to my library" and then you can add gog games to your steam game menu and start the games from there

So what's that, then, just as long as I have them downloaded?

In other words, no. lol

Adding games the way Gyro explained doesn't tie them to your account, it just puts the pre-installed game on your games list and shows your friends what you're playing. The only real benefit is being able to talk to your Steam friends in-game, but many games don't work with the Steam overlay (any DOSbox game, for example).

That's wrong for a start. DOSBox games work fine with the Steam overlay, just as long as you use OpenGL output (configurable from the config app or from the .conf file). There are numerous games on Steam that also use DOSBox (Commander Keen, Dark Forces, Wizardry) and use the Steam overlay just fine.

The only things you'll be missing out on in Steam are the achievements, trading cards and cloud saves (assuming that the game supports these three).

Now what is true is that some games - mainly early 90s Windows titles - will not work with the Steam overlay owing to the fact that they use DIrectDraw or Direct3D pre-DX7, but buying the same game from Steam wouldn't remedy that (Jedi Knight, for example).

If you decide to use Steam to launch non-Steam games (like I do, incidentally), you should know about a bug or whatever that can occasionally remove all non-Steam shortcuts from the Steam library. It only seems to happen (and not always even then) on controlled PC shutdown when Steam is still running; if you exit Steam manually before turning the computer off, everything seems to work fine. Crashes and hard resets haven't caused any Steam-related problems to me.