is an expression that combines the 副詞（ふくし） (adverb) 全（まった）く, with a phrase that uses another word in its ない form. It is often translated as ‘not at all (A)’. Literally, it is closer to ‘completely not (A)’, or ‘entirely not (A)’, coming from the kanji 全（ぜん）’s meaning of ‘whole’.
Like many other adverbs, まったく may be used at the beginning of a sentence, or directly before the word that it is describing as being ‘not at all’ (A).
This dog does not bark at all. (子（こ） may sometimes be used about pets, if it is obvious what is being discussed)
Even if I did get complimented by you, it wouldn’t make me happy at all.
The shopkeeper said 'This fan is very quiet', so I bought it. However, it was not quiet at all.
I don't have any muscles at all, so I can't carry this by myself.
It is common to see this expression using both the kanji form, and plain hiragana form of 全（まった）く, so both should be learned early.
まったく is very similar to 全然（ぜんぜん）
, another grammar point that is used to highlight the complete lack of something. However, まったく tends to sound a little bit more serious, and is therefore more likely to be used in formal writing/situations. 全然（ぜんぜん）
on the other hand is far more common in casual speech.
I don't understand at all, so please help me.
I have no clue. Can you help me?