Remember this-comma + verbing phrase is an
action modifier. In simple terms, when you see a comma + verbing phrase, think of it as explaining the "
(A) how" aspect of the
preceding actions or "
(B) the result" the
preceding actions. It further
adds information about the previous action.
Here, the main action is,
Sal applied himself in his new job, now the following comma + verbing phrases are
adding a description to "how" he applied himself to his new job. The case
(A) applies here.
Modifier, in simpler terms, means something that adds more information about something, there are different types of modifiers, like adverbial modifiers, verbing modifiers, verbed modifiers, they all do one thing- add more information to their respective entities.
Eg 1: My car,
which cost me around $25,000, broke down yesterday. Here, the "which phrase" is a relative pronoun modifier. It is modifying (or adding more information) its noun "car" by giving information about the price of it. The main meaning of the sentence is- My car broke down. But, by incorporating the relative pronoun modifier, I am adding more description to my car. So that's how modifiers work in general.
Eg 2: Bunuel has contributed to the GmatClub community like no one has,
cementing his spot as one of the legends of the platform. This is an example of case
(B), when the comma + verbing gives the result of the previous action. In the sentence, Bunuel contribution to the community
has led to him becoming a legend in the community.
Eg 3: Stephen Curry drained 4 threes against Utah last night,
surpassing Reggie miller on NBA's all-time 3-pointers made list.
P.S: There are other nuances associated with the verb-ing modifiers, such as the "doer" of the modified entity and modifier must be the same. To study that you can have a look at this detailed article
https://gmatclub.com/forum/verb-ing-modifier-conceptual-clarity-151205.html#p1214284.