when to use j' vs je

Willow, 

the lesson doesn’t go into detail about which words start with h muet ( silent h) or with h apsiré, although j’habite ( no ‘s’ at the end of this) is given as an example with a silent h with elision.

The links below provide more information on elision and silent h and h aspiré. Basically you are best to learn the words as you go along.

 However, if the word starts with a silent h, as the verb habiter does, you will elide giving j’habite, for example. If it starts with an h aspiré, as another example the verb hanter does, there will be no elision, giving ‘ je hante ‘. 

https://www.lawlessfrench.com/pronunciation/elision/

https://www.lawlessfrench.com/pronunciation/h-muet/

 https://www.lawlessfrench.com/pronunciation/h-aspire/

 https://www.lawlessfrench.com/verb-conjugations/habiter/

 https://www.lawlessfrench.com/verb-conjugations/hanter/