While editing an interface object in Appian, you can add test data into your rule inputs by selecting the Test button. This feature allows you to simulate how the interface would behave with specific inputs, facilitating a more efficient and accurate design and debugging process.
Reference:
Appian Documentation: Testing Interfaces

When configuring a Write to Data Store Entity smart service node to write a new row to a CDT's corresponding database table, you must specify the data store entity where the CDT is stored. Additionally, you need to provide an input of the type that matches the CDT, in this case, an input of type ACME_video, which will contain the data to be written to the database.
Reference: Appian Documentation - Write to Data Store Entity Smart Service

In Appian, the data type of a local variable is inferred from the value it is set to. Unlike some other programming languages where the data type must be explicitly declared, Appian determines the data type automatically based on the initial value assigned to the local variable. Local variables in Appian are quite flexible and can store various types of data, including complex data types, not just primitive ones.
References: Appian Documentation - Local Variables

The best practice in Appian for passing values into an interface is to use named parameters, which is demonstrated by Option B. Named parameters make the code more readable and maintainable by clearly specifying which parameter each value is being passed to. In this case, the recordId and firstName parameters are clearly being assigned the values 1 and "Kyle" respectively.
Reference:
Appian Documentation: Passing Parameters to Interfaces