You don't mention what language you're taking about?.
But assuming it's assembler?, an instruction is something the processor can run, a directive is an instruction to the assembler (and nothing at all to so with the PIC).
This piece of assembler directives checks if a name 'TXINV' has been previous defined, if so it defines two lines of code one way, or if not it defines them the other way. This enables you to use an inverting, or a non-inverting output, by simply defining (or not) a single name at the beginning of the program. It's from one of my new Manchester radio tutorials.
Your example didn't include any code at all, so wouldn't produce anything.