Same syllable, four meanings
In Mandarin 'ma' said with a flat, rising, dipping, or falling tone means four different things — mother, hemp, horse, or a scold. Tones aren't decoration; they're part of the word, so 'nǐ hǎo' only means hello with the right melody.
Tone carries meaning
Mandarin has four main tones: first (flat, mā), second (rising, má), third (dipping, mǎ), fourth (falling, mà). The same syllable means different things depending on tone.
Nǐ hǎo
你好 (nǐ hǎo) means 'hello' — literally 'you good'. Both syllables use the third tone.