Hello Bob,
There is manual that comes with the game in PDF format. It will be found somewhere in the game files you have saved on your computer.
The Nuke issue may be related to rules set up. When you set up your game, have you checked off the "Allow Nukes" option in the game rules dialog? If you have not, you can still build Nukes, but they don't do anything. I come across that all the time in games I play against the AI. It build nukes if it gets a city with SN or LN specialty, but then never uses them, as it cannot detonate them as nukes.
As to the Drop command, not sure on the whole issue. I can say that you cannot drop Armor from an Air Transport, you can only drop infantry (aka, they become paratroopers). So, your Air Transport can carry Armor, but it needs to land to offload.
For the Trucks with a Heavy Artillery, I use these all the time to ferry the HA around. I drop them into Forts as a relatively safe place to fire from. If I am remembering the rules correctly, you need the ability to stack units turn on to be able to drop a unit in the same square. If unit stacking is turned off, then you might have the issue. By default, stacking only occurs in cities.
Hope that helps,
Cheers :)