like when i want to install my games i just click on the install file when i am offline

Oh, actually, I think I have just got it. What you mean is you use Galaxy to install your games, and now you want an installer. In which case, under one of the Galaxy options is the ability to download offline installer - I don't use it so can't help there. Alternatively goto this website, into your games account, and find the game. Under the game below the galaxy installer option is an expandable bit with Offline Backup Installers. You can download the files there.

like
you know when you pirate a gog game they put it in those installation folders

how do i do that

and i apologise english is not my first language

Just updated.

Have you downloaded the offline installers? If so, just put them in a folder of your choosing then click the install button and you're good to go.

EDIT: Ninja'd!