Welcome to the fun
There are numerous places to get information. It all depends on what you want to do. I suggest you start by reviewing the SDK. It's dry and will put you to sleep, but shows alot of what can be acomplished.
Pick a "thing" you want to do like terrain, scenery, effects, missions aircraft/guages.
Understand XML - just the basics.
You must have the Deluxe version of FSX to get ths SDK. Otherwise download FS2004 version.
Search the wiki here for information.
Many other sites have forums and tips and tutorials.
What I did when I started was to create some terrain using Canadian CDED data. Worked out quite nicely. I then moved over to GMAX to create scenery. Just small building etc.
Two of my favorite sites for tutorials are:
http://www.windowlight.co.nz/design.html
http://www.freeflightdesign.com/
For information on the technical stuff of air files.
http://pagesperso-orange.fr/hsors/index.html
Then DO THE GMAX TUTORIAL that you download from turbosquid. It may seem strange to do the character and game level tutorial, but you will use all the things they teach you there, so that you can work with more complex scenery and building your own aircraft.
After playing around, you come back here post a question and keep plugging away. I suggest scenery first because GMAX is very frustrating and getting scenery to work is easier than starting with an aircraft right away.