Some languages, famously Chinese and other Eastern languages, utilizes tones to distinguish between lexical and grammatical meanings of words. These tones are simply changes in pitch that inflect the words to have a different meaning.
This is one of the ways that tonal languages can expand their lexical scope, without adding new words. Instead, the lexical capability of the language is expanded through altering the pronunciation of the same word. This is one of the foremost troubles amateur and beginner speakers of tonal languages face, correctly inflecting the tone of the word to match the intended meaning of the word.
If the speaker incorrectly inflects the intended tone, the meaning of the word can change dramatically resulting in confusion. This is considered to be much worse than grammatical mistakes in English as many Chinese speakers only loosely associate the root words (without the tones) together as the tones change the meaning so significantly.
When writing tonal words, the Chinese use contour to show internal pattern of rising and falling that the word undergoes with the pronunciation. This is the predominant method of writing tones for Eastern languages. African languages on the other hand, use the register system that distinguishes tones based on their relative predominance to each other.
All in all, tones are an intuitive way of distinguishing meaning between the same words, and not normally relevant in Western languages. If you’re planning to learn a new language, be sure to keep these differences in mind.
Below is a link to a beginner video on the four tones of Mandarin.