FarApp configurations will occasionally need the internal ID (sometimes referred to as IID) of certain objects in NetSuite like orders, forms, customers, items, and more. NetSuite can be configured to display the internal ID through various means (see this article for one option https://support.farapp.com/hc/en-us/articles/360041237633) but you can always locate the internal ID of an object in the browser address bar when viewing that particular object.
For example, the screenshot below is the view of a customer in NetSuite.
In the browser address bar you can see id=XXXX, where XXXX is the internal ID.
In this case, 3018 is the internal ID of the customer you are viewing.
The same is true of any object you view or edit in NetSuite with the exception of new objects that have yet to be saved. NetSuite will assign the internal ID to the object once it has been saved for the first time.