Importing the package

It might be required for you to import the package if you encounter any issues (like casting an Array), so better be safe than sorry and add the import.
import crafttweaker.formatting.IFormattedText;

Creating an IFormattedText Object

You can always defer an IFormatted Text from a String (the conversion is automatic).

Using an IFormattedText Object

You can add or concatenate two IFormattedText together using the respecting Operators: + ~

Besides that you can use the IFormatter to format an IFormattedText Object.