Temporal words are words that are used to show how time passes, or how a series of events move sequentially when elements in a story are being brought together.
Temporal words are time-related. They function as helpers and prompters for the next series of events. Even though the majority of temporal words consist of one word -usually prepositions- (e.g. on, by, before, after, etc), some phrases (e.g. after that, soon after, before that, etc) also function as temporal words.
In essence, temporal words help to show how time passes, or the position an event occupies in the sequence of things.