How do I make add-ons?

ok prolly a stupid question but im a n3wB.. I want to learn how to create my own planes for FSX. I looked on the utility page and got confused really fast.. If someone could tell me exactly what programs i need i can get them and start but im just not sure wich ones will work for FSX and i dont want to spend the money to get them only to find out it wont work for FSX. thx
"Beware the Fure of a Patient Man!".......John Dryden
"Beware the Fure of a Patient Man!".......John Dryden