Hey! I'm new to GOG and I'm curious how's the achievement hunting on GOG. Anyone care to explain or give me a link to a video?

I don't even know what achievement hunting is.

Achievement hunting means that you try to earn all the achievements of a game.

Explain what? A video showing what? What you are trying to ask is not clear.

here:
https://www.youtube.com/watch?v=dQw4w9WgXcQ

That actually is a good question. Do GOG provide some kind of guide/explanation what functionality does Galaxy provide and how all of it works?

Edit: well, there is some info on Galaxy download page, but it lacks details.

Not to sound like an ass, but I know I still do. You play the game and you get achievements if the game supports Galaxy achievement. Otherwise, you get to only play the game. It's not like there's some huge secret there.

If anyone needs achievements to play specific game then it's a bad game.

And let`s not forget that some games bring their own archievements, independent from Galaxy. You can even earn them when playing offline. Drox Operative, for example.

Self-Promotion-Time:

There's a thread that keeps track of those games (and there was also a GOGmix, before GOG decided to drop a bomb on the feature)