From: Chicago, Illinois
They are actually pretty simple; if you are having difficulty executing them, it may be because you are not trying in the correct phase. IIRC, both are in the movement phase, but I am not 100% sure. Just check the units to make sure the "DROP" or "INVADE" buttons are active. A few tips:
--Keep alot of transport aircraft near, or in the same hex, as the Para unit. If you are Soviet, you will need all the lift capacity in the VVS to drop 3 Para Bdes. Also, you can't airdrop Airborne Guards Div.
--Note that brigades are likely to drift; accuracy is an issue. Be prepared for disasters, or drop multiple units if you really want a particular hex
--Overall, I think Paras have limited usefulness for Soviets; mostly to cut a retreat path when you are attempting a breakthrough
--You need a couple turns to plan; park Para on airbase, pick the hex you are planning to drop on, and wait for the prep to rise above 50. It rises pretty fast, so you may as well wait until it's 95
--Stack 1 or 2 division in a port with the Amphib unit; pick an invasion hex, and prep for it
--Prep for Invasions is very slow; if you use 2 divisions, it will take a long time, because the only decent port is Sevastopol. By the time you get Odessa, you probably don't need to invade things. Also, it's Black Sea only
--Recon ahead before you land in a port hex. A good Axis player will build a Fort Unit in every port for this reason, and you don't want to land on that.