Okay, first, let's tackle the fact that you are dealing with three distinct vocab issues:
- 'Signifier' is a semiotics term.
- 'Enunciation' and 'utterance' are specific to the author's (Zizek) and the author's subject (Fink, Lacan, van Haute), other authors' philosophical distinctions.
- 'Ne explétif' is a French grammatical term which uses a particle which has no direct analog in English.
And also, you might be short some background information about the nature of Cartesian duality and various ontological positions regarding it. I don't know if you're familiar with the distinctions of subjectivity, objectivity, and intersubjectivity. In short, under naive realism, one takes a metaphysical presumption that there are material and abstract ontologies or domains of discourse and then tries to understand how and if they relate. In fact, this wrestling with dualism is one of the central themes of Western philosophy going back to the Pre-Socratic Greeks.
Remember, the important thing here are the skills at play, some of which only come from studying philosophy. For instance, familiarity with German idealism, Gottlob Frege's antipsychologism and founding of the analytic tradition, and then Freud's revolutionary psychoanalysis might help you to see some themes and ideas at play. (I'm fond of the Hegelian dialectic.) If you're finding philosophy difficult to read, pick up an intro text and an intro history and read those first to get some bearings. Philosophy extends back from Anaximander and his ilk to current philosophers who have been wrestling with many of the same questions for 2,000+ years.
Also a book on introduction to linguistics will help shed light. I have an older copy of Linguistics for Non-linguists: A Primer with Exercises which is a good basis to understanding how language works including looking at phonology, pragmatics, grammar, etc.
Now, on to your specific question:
A signifier is a symbol that stands for something that is signified. Hence the word 'cat' is that which stands for a cat. It needn't be 'cat' as 'gatto' in Italian accomplishes the same feat. It's related to Ogden and Richards' ideas in The Meaning of Meaning, particularly 'symbol', 'reference', and 'referent'.
As for 'ne explétif', we are dealing with a sound that is not an independent word that adds meaning or semantic content to a phrase. In French, 'Je ne suis pas un poisson' means 'I am not a fish', and here 'ne + verb + pas' functions to negate the verb. In 'Évitez qu’il ne vous voie', 'ne' adds emotional overtones of being bad or fearful. In English, we might use a phrase or another sentence. There's a difference between 'Don't let him see you' and 'I swear to God, don't let him see you, or you'll be sorry', the latter communicating urgency. The French do it with 'ne' according to the rules listed in the citation above.
As for the difference between 'utterance' and 'enunciation', in common parlance, an utterance is anything said and refers to the objective, phonological nature of language. 'Whoooooooa!" is an exclamatory utterance, and 'I'm here' is a declarative one. One pronounces those written words in a particular manner, and if one does so well, one is enunciating. So, understand the difference between pronunciation and enunciation first. But as is often the case, philosophers often repurpose ordinary language with technical meaning. Now, we are in a position to unpack Zizek's text!
"Lacan, having carefully distinguished between the two sides... enunciation versus utterance... that the ne explétif... signals a moment in which the subject.... brings itself into view.. of how it positions itself with respect to the meaning..."
What he is saying is that the particle 'ne' indicates the speaker's propositional attitude about the positive aspect of the proposition. This then lays bare the dichotomy between the objective (positive) aspects of a representation and the subjective (normative). Ne indicates that the speaker thinks the objective situation is bad or that she is fearful.
This is later born out where Zizek writes:
"for Lacan, an 'I' is 'designated' when there is no gap indicated between enunciation and utterance, where as 'I' is 'signified' when there is indeed a gap indicated..."
where that gap (difference) between the act of enunciation (signified) and utterance (designated) is nothing more than describing whether a proposition is normative (uttered, designated, subjective) and positive (signified, enunciated, objective). Think about it in English. There's a fine distinction between:
- "There's a shark in the pool."
- "Awesome! There's a shark in the pool."
- "Ahhhhhhhhhhhhhhhhhhh my legs!!! There's a shark in the pool."
Now, I more fully see your struggle with vocab. To improve your philosophical reading comprehension, you need to expand your skills in dealing with the historicity of philosophical terminology, your understanding of linguistics, and your ability to use references independently of others to arrive at these sorts of conclusions. This is NOT an easy task. It's work, work, work! There is no golden road to philosophy.