(Important!) To play the mod you will need the full version of Wolfenstein 3D!
Setting up:
If you downloaded the file successfully, then extract it's content anywhere you want. It should have these files in the folder:
-ecwolf.exe
-ecwolf.pk3
-SDL2.dll
-SDL2_net.dll
-W3DFE.pk3
-W3DFE_credits.txt
If everything's present then look for the WL6 files in your Wolfenstein 3D's directory and copy them in the mods folder.
Starting the game:
If everything is done as described above then all you have to do is to click and drag the W3DFE.pk3 file to ECWolf. (If you also have Spear of Destiny present in ECWolf's folder then it would ask you to choose from the main games. In this case choose Wolfenstein 3D.) Then the game should start in a few seconds. Enjoy. :)