I don't want to be mean, but if you've running Linux for many years, you should know how to troubleshoot such an easy one...
1) Download the Linux package of the game and extract it
2) Open a terminal,
cd
to the directory where you extracted your files, and run
./nw
or
./launcher.sh
You will get an error ("Permission denied"), which is to be expected, because distributing a Linux package of a program/game as ZIP or RAR archive is a bad idea, because it doesn't preserve any file permissions. Therefore you have to make sure the main file is executable
3) Make
nw
executable by typing
chmod u+x nw
4) Run
./nw
(or
./launcher.sh
) again
5) If you still got errors (i.e. missing libraries), make sure you have all the needed libraries installed
(I'm not going to explain how to install additional libraries, this is way to off-topic)
6) After installing the missing libraries, the game should run perfectly fine