The adverb 务必 is used to emphasize that an action must be performed.
In a sentence, it is placed before a predicate that is expressed by a verb.
You must get there on time
nǐ wùbì yào ànshí dàodá nàlǐ
Please be sure to attend tomorrow's meeting
míngtiān de huìyì qǐng dàjiā wùbì chūxí
The number of seats is limited, so be sure to book them in advance
zuòwèi yǒuxiàn, wùbì zǎorì yùdìng
The adverb 万万
The adverb 万万 is mostly used in negative sentences.
It is usually followed by the negative adverb 没 or 不 .
This combination has the meaning "under no consideration" and emphasizes that an action doesn't need to be performed.
When you leave your house, never leave the gas on
wànwàn bù néng kāizhe méiqì chūmén
He never thought he would succeed
tā wànwàn méi yǒu xiǎngdào tā huì chénggōng
My boss offered me a salary that I would’ve never dreamed of
wǒ lǎobǎn gěi wǒ tígōng le wǒ wànwàn mèng xiǎngbudào de gāoxīn