Hello. I have tried to install the game now but it gets stuck on a certain point that i have no idea how to do anymore. It gets stuck at:
Content/content10/bundles/buffers.bundle


It also opens up a new tab where it wants me to do something but i dont know what, anyone with similiar problem? i tried with google but i dont find many usefull things.
i have 4 discs available, i put in the first one only for this to happen.

Hard to say. You could use the Game Key (in the manual I think) to unlock the game as download here, and then use the download to install.

http://www.gog.com/redeem

Hello, Yes i have used the game key But i dont understand how i download it, it just shows up as VLC for me? am i doing something wrong?

Iy you are using your browser you need to download all 7 files (1 exe-file and 6 bin-files (Windows wants to open with VLC). Download all parts and double click the exe to install. Same for the patch (2 parts; 1 exe and 1 bin-file). Download both and double click the exe to install.

Account - Library - Witcher 3 - left side of the "pop-up" are the files.