Cantonese 得 (dak1): saying how an action goes
Cantonese has no separate word for quickly or well. It reuses the adjective and hooks it onto the back of the verb with 得 dak1, so 佢行得好快 is they walk very fast.
The adjective does the adverb job
English builds a second word out of the first: quick becomes quickly, good becomes well, slow becomes slowly. Cantonese does not bother. It takes the same adjective and attaches it behind the verb with 得, and the meaning shifts from describing the thing to describing the action.
The degree word stays
A quality on its own sounds unfinished in Cantonese, which is why 好 sits in front of it in a plain description. The same applies inside this pattern: 佢行得快 sounds clipped in a way 佢行得好快 does not. Swap 好 for 太 or 幾 exactly as you would elsewhere, as covered on the degree page. For the negative, 唔 goes after 得: 我瞓得唔好, I slept badly.
The same character does a second job. In 食得晒 it sits between a verb and its result and asks whether you can manage the thing, which is the potential complement on its own page. Two quick tests tell them apart: the manner 得 is always followed by a quality, and the potential 得 is always followed by a result such as 晒 or 完. If an adjective comes next, you are in this pattern.
Common mistakes
Leaving 得 out
佢寫好靚 puts a verb and a quality next to each other with nothing joining them. 得 is what connects the two: 佢寫得好靚.
Putting the quality in front
佢好快行 describes nothing. How an action goes always comes after the verb in this pattern.
Dropping the degree word
佢行得快 is not wrong so much as unfinished, in the same way a bare adjective is on the adjectives page. Put 好 in and it lands.
