The type of media that is most likely to accompany a text describing how to put a piece of furniture together is illustration.
Texts that give instructions, which are generally known as manuals, usually resort to illustrations in order to guide the reader in a more effective way. In other words, illustrations make the information presented easier to understand since they generally indicate all of the steps that the reader needs to follow and the order in which the steps must be performed. In that way, a text that describes how to put a piece of furniture together, which will include different steps, is most likely to be accompanied by illustrations.
