Hi alfredo091950, sorry to hear your having so much trouble using the c172p.
First let me say there is usually some configuration needed in order to get FlightGear and your hardware to work correctly together. Ask specific questions and I am sure there are users that will help with support for your issues.
There are multiple ways of starting the engine in the c172p engine. Under Aircraft Options there is "Autostart", that will start the engine easily without having to do anything. There is also a choice for having the engine running on the next startup of the simulator, automatically.
If you choose to start the engine manually with the "realistic" steps needed to start an engine in real life then your expected to know how that is normally accomplished.
Under "Help" there are tutorials, one of which details the steps needed to start the engine manually. It will take you step by step through the startup process.
The core of the program (fly) DO NOT WORK FOR ME
I assume your talking about the built in launcher, we refer to it as the QT-launcher. Again, there is certain steps you have to take in the launcher before the "Fly" button will become active. One of then is to select the aircraft and location you want to fly from.
I just read this and was unaware of this feature. It is potentially an issue you might be seeing with your "Fly" button.
I thought maybe because I had an older version it wouldn't allow me to start (2018.1.1) but after installing 2018.2.2 it was the same.
It took me some time tinkering around and going through screens when I saw that the plane I had selected had an "Update" button next to it. After I pressed that, the Fly! went white.
See
FG would not start
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