They process information in radically different ways. Order, on the one hand, comes from the Latin ordo, ordini. Order implies linear, rule-governed activity. Order is imposed from without. Structure, on the other hand, comes from the Latin struere.
Structure emerges from within.
Clustering should help you find and generate ideas and, having found them, to structure and restructure them long before any ordering actually takes place. Clustering is a technique for collecting thoughts around some stimulus, for finding a focus, and for allowing a sense of the whole configuration to emerge even though all the details are not yet apparent. Clustering is a technique for engaging and utilizing the raw materials of one's experience and giving them a tentative shape. In short, it is a discovery process. For brief journal entries, clustering is a simple process taking thirty seconds to two minutes, just long enough to let ideas spill out onto a page until an idea presents itself that you can develop into a whole.