Using the Incendiary Grenade in AAO is relatively easy. All you have to do is pull it out and throw it by pressing the fire key and releasing it. 4-5 seconds later it will blow up and start to flame. The blast radius is smaller than that of a frag grenade but it will kill anyone who walks over the flame.
Cooking incendiary grenades
Cooking a nade is one of the coolest things to do to surprise your enemy. When you cook a nade you are pulling the pin by pressing the fire and alt fire keys and holding the live grenade in your hand for a few seconds before you throw it by pressing the fire key. Usually the opfor you are throwing it at can hear you cook the nade and run away, but if you pull the pin before you are close to them they won't. A good rule of thumb is only cook it for 2-3 seconds because some nades have shorter fuses than others. Also try blowing up the Blackhawk in SF CSAR with a cooked incendiary grenade that way if you die the nade will still go off and blow up the Blackhawk.
Kamikaze incendiary grenades
We have all seen the kamikazes who run into a room known to have opfor in it with a nade in their hand. The proper way to do this is to cook it long before you enter the room. The opfor will know you have a nade in your hand due to how you look. The more the cooked the better chance you have at taking them out with it and burning them alive!
Airbursting a nade is a great technique to use to blow up before it hits the ground. You cook the nade like normal, but you throw it higher so that it will blow up in the air over your target.
You don't shout anything when throwing incendiary grenade so alerting the enemy should not be a problem.
Ah yes... That wonder CSAR. You secure the chopper, and throw your thermite into it and...it ricochets back at you, hits you, and misses the Blackhawk and kills you in a matter of 4 seconds ... Double the Humility. Well, for all of those people who have ever missed the Blackhawk, This is for you. By rolling a thermite into the Blackhawk, it won't ever EVER EVER come out. Ever. It stays and does its job. Otherwise, I don't recommend wasting your thermite on an OPFOR because you might need it later!
Thermites can also work as smoke grenades, as they give out black smoke. I wouldn't recommend walking through the black smoke though.