An analogy to building a brick house is useful here. To build bricks, straw and sand have to stick together. Then the bricks are held together with mortar to form walls. The house has structure when the walls are arranged in certain patterns. Different organism groups in the soil foodweb do the same for soil structure.
Bacteria glue the clays, silts and sands together into microaggregates.
Microaggregates are bound together by fungal hyphae, root hairs and roots. The structure of the rooms are made by the arthropods, insects and earthworms. Only when all the organisms are present and active can roots and water move into the soil with ease. Soil compaction is a major disturbance of soil aggregation. When heavy machinery moves across the soil, the pores and channels within the soil collapse.