We have previously answered this in one of your other threads - in general, you will want to look at the property tree, especially at the /position, /orientation and /velocities nodes. There is also a dedicated /fdm node.
The Nasal bindings to access the property tree are primarily getprop/setprop, and props.nas for an object-oriented interface:
http://wiki.flightgear.org/Nasal_library#getprop.28.29http://wiki.flightgear.org/Nasal_library#setprop.28.29http://wiki.flightgear.org/Nasal_library/propsAs we said, things are slightly different for AI/MP aircraft, because you don't currently have access to an actual FDM, autopilot or route manager instance there.
http://wiki.flightgear.org/Howto:Workin ... propertiestanker.nas is basically what you need, but using that makes only sense if you understand how the property tree is used, and how the data there relates to Nasal variables and vice versa (you cannot necessarily access all variables via the property tree, and you may not necessarily always want to use the property tree for your variables either).
Again: You will definitely want to make sure that you understand how the property browser and Nasal console work, before writing any real code. Otherwise, it will not make much sense to you.