For questions about Chinese prepositions, some times also called coverbs, e.g. 在，往，对, etc.
Prepositions (介词) are words that precede other nouns and express their location in space or time.
Chinese prepositions often introduce complements of location, direction, time, etc. Some common ones are 在，往，向，对，从，给，etc.
According to some interpretations (among which Wikipedia), coverbs, which appear in constructions with verbs in series, also have prepositional functions.
Feel free to use this tag either when referring to prepositions or coverbs, or also when asking about how to render a specific preposition or prepositional phrase in Chinese.