NZFF

How do you open fsk sdk???
I have it installed but can't open anything.
Also is it hard to use?

The SDK is a collection of tools, and information in HTML format. If it is installed correctly you'll have a folder in Microsoft Games called 'Microsoft Flight Simulator X SDK'
Start with the 'sdk overview.html' document.
EDIT: Oops, almost forgot -- in my experience even with some serious reading, the SDK is almost impossible to use without some other sort of resource, such as the scenerydesign.org site.

Yeah they don't make it easy, the SDK is usually the foundation where third party developers create tools like FSDS and scenery design programs.

Yep it depends what you want to do but each series of tools is in a sub folder. IF you have specific questions we may be able to help but the tools are too expansive and far ranging to write a complete overview....even the SDK documentation struggles to fufill this task!

Ok

I have opened the sdk overview buy i can't work out what to do then. It talks about all this stuff that i suspect is in a different part of the program. All i want to do is make a simple flight plan or to so i can have modern 737 fly from wellington to auckland etc.

At this stage for AI flights you are better of using the tools for FS9, create the BGL file for flights and then copy it into FSX. It will work fine until X specific software is developed. Just remember in your flightplan to ensure the FSX aircraft the flightplan is looking for is in the plan.

Are there any easy to use tools that even i can use??

Depends which one you use, try one called easy AI I think its called, search avsim or flightsim, plenty around.