First, makes certain you download the correct version. The two different versions, one for FSX/P3Dv3, and one for P3Dv3 and up.
Once you have the zip file on your HD, unzip it to a TEMP folder you've created just for this purpose.
Copy all the folder resulting from the unzip, and I can't speak to the exact name of the plane's folder, since I don't have P3D at all, but the one for FSX is named FA-18C_FSXBA_BA_18.3.00. Copy this folder to where you have all your airplane folders. In FSX it's ...\FSX\Simobjects\Airplanes . I believe in P3D it's something similar.
Go to the plane's folder you just installed. Open the folder named P3D Specific Files. Under that is one named Gauges. Open that folder, and copy all the files in it to your ...P3D\Gauges.
Clost the Gauges folder, and open the one named Panel.Fleet, still within the P3D Specific Files folder. Copy the 2 files within that to the folder Panel.Fleet, in the plane's main folder. You may be prompted to over-write the files already there. Answer Yes.
Now, go open the folder named EXTRAS, within the plane's main folder. Open the folder named EFFECTS. Copy all the files within it, along with the folder TEXTURES, to your P3D Effects folder. You will be prompted to merge the Textures folder with the one in the P3D\Effects folder. Answer YES.
If you are prompted to over-write any of the files within the Effects folder, answer Yes.
Now, if you desire to save some HD space, go to the TEMP folder you created at the beginning of this process, and either delete it, or it's contents. I strongly advise keeping the original Zip file you downloaded, in case you need a back-up copy of any of the files it contains.
Does this help at all?
Pat☺