The best way to do this is to lay the barrel on its side on a table or bench to get it closer to waist height. If you have a partner who could help that would be ideal but if not proceed anyway. Place the spigot and one washer on the port and push the neck into the hole. Ask your pal to hold the spigot in place while you reach into the barrel and put the washer and nut onto the neck and hand tighten as much as possible. If there is no one to help,  turn the barrel so the spigot is face down on the table, this will hold it in place while you reach in and tighten washer and nut onto the spigot neck. Ratchet down tightly on the nut to seal the spigot. (the spigot does not thread into the hole, place it in and use the washers and nut to create seal).