Ok let's see: (By the way: Which version of 3DGS do yozu have?)

1: You have a project folder. To this folder you copy the newton.wdl, the newtonscript2.wdl, and the newtonsplash.tga.

2: Search in your 3DGS directory. there is a folder named acknex_plugins. If it's not there you don't have the latest version of 3DGS but that's no problem, just tell me then.
To this one (if you have it) you copy the newton.dll

3: If you already have a level open the mainscript of it. If not create a new one and create a basis script for it.

4: Over your mainfunction you put in those lines:
include <newton.wdl>;
include <newtonscript2.wdl>;

string level_str = <levelname.wmb>; //don't write it twice if it's already in your script!!!

ifdef USE_NEWTON_GAME_DYNAMICS;
string newtonLevel_cls = <levelname.CLS>; //same name as levelstr
endif;

5: Your main function should look like this in the beginning:
function main()
{
wait(3);
level_load(level_str);
ifdef USE_NEWTON_GAME_DYNAMICS;
wait(1);
dll_handle = newtonHandle;
temp = NewtonAddMap (level_str, splashscreen);
endif;
sleep(1);
splashscreen.visible = off;
//...
}

6: Now Newton is initialised right and you can create Newtonobjects by giving them the function Newtonwoodentity and setting their Skill1 to a mass parameter. Just follow the manual for more complex stuff.