We know it’s overwhelming, but you are more likely to get quick responses if you break these questions down into separate posts/subjects.
In any case, I will try to touch on some of the points:
What does the first four similar lines of every script do…?
See comments below
# imports Common Language Runtime library .This will serve as a bridge between python and the .NET wold
# See this: http://ironpython.net/documentation/dotnet/dotnet.html
# Loads the Protogeometry dll (.net assembly) so Python can use it
from Autodesk.DesignScript.Geometry import *
# Imports Geometry Classes from the DesignScript assembly (Protogeometry)
# this gives you access to Dynamos built in Geometry classes and more.
dataEnteringNode = IN
#The inputs to this node will be stored as a list in the IN variables.
# you don't actually need this. go ahead and delete it, nothing will change/
# The data you plug into the inputs will come as the IN variable
b. why should i import revit modules when I open and work on a console inside revit?
The python script runs inside a scripting engine, embedded into Dynamo, which has it’s own context, so tou still need to load the references you will need to use, and you need a “handle” for the revit/document instance so you can refer to it.
c.What exactly do i do when starting a transaction?
In fact, you should read the entire Developer’s Guide if you are planning on diving deeper into the API:
a.Where can I find the list of modules Pre built inside API…?
You can download the Full api doc from the official SDK (google revit API SDK), or use revitapidocs.com
b.can u explain how to read data from Revit ,for instance if i need to script
to increase door width if <3’(say parameter name ‘W’)
You should post a separate post for this