In English grammar, prepositions are words that show the relationship between a noun or pronoun and other words in a sentence. They indicate location, direction, time, manner, or other relationships.
Examples of common prepositions include:
Words of location: in, on, at, by
Words of direction: to, from, up, down
Words of time: at, on, during
In the sentence "Any decision taken at the right time will help to solve the issue," the word "at" is a preposition indicating the time when the decision is taken.