, seen primarily in hiragana, is an adverb that indicates that (A) has or will ‘finally happen’. In many cases this is after some state that has been continuing for a long time, or has been compounding further and further until (A).
Like many other sentence altering adverbs, いよいよ
will appear at the beginning of a phrase. It is also considered quite casual when compared to other grammar points like ついに.
Tomorrow is finally our graduation, isn't it…
It is finally my turn. I am nervous, but I must do my best!
highlights something that is compounding, it can also frequently be translated as ‘more and more’.
As the typhoon approached, the wind started to blow more and more.
Listening to his story makes him more and more suspicious.
The difference between the nuance of いよいよ
being ‘finally’ or ‘more and more’ will usually be clear due to the statement following it being either conclusive (finally), or inconclusive (more and more).