Bonjour Harris,

The lesson that you are working on is a level B1, the «ne explétif is covered in level C1 and is seen primarily with le subjonctif verb conjugations.

Here is the lesson if you are interested:
Understanding the 'ne' explétif%252Fsearch%253Fs%253Dne">Understanding the 'ne' explétif

That being said, if you are studying at B1, I wouldn't concern myself at this point with C1 lessons other than to familiarize with the «ne explétif» because you will probably run across this again several times before beginning the C1 level, primarily in examples.

J'espère que ma réponse vous aidera.
Bonne chance et bonne continuation dans vos études en français, la langue de Molière.