Hi Sachin,
GuiXT mimics what the user can do manually on SAP Front-end. There are two aspects to GuiXT customization - one is the design/redesign of the screen elements, and other is saving of the data - mapped to actual SAP field elements in the database. There are consecutively two kinds of scripts - one for design and another for input/save.
To answer your question, Yes, you need to capture the steps of data transfer into a script (which can be generated via a recording function).
For better understanding, let me point you to an overall scenario in action - Simplify Sales Order Creation (VA01) in 60 minutes
If you need additional direction/help, I'll be happy to guide.
Best,
Vishal