Remember, the plug ins aren’t created by Ambrosia, so we can’t guarantee their performance.
First read the Read Me file that came with the plug in. Some of them have special instructions to get the plug in started. If there are no special instructions, then just place the plug in itself into the plug ins folder, and launch the game. If you still have a problem, then the Read Me file should also have a way to contact the author of the plug in.