What is the difference between spores, culture, spawn, and substrate?

Spores are the seeds a mushroom drops, and germinating them gives mixed genetics. A culture is living mycelium of one selected strain, kept clean on agar or in liquid. Spawn is a carrier such as colonised grain that spreads that mycelium into bulk. Substrate is the final food, for example straw or supplemented sawdust, where the mushrooms actually fruit. The usual order is culture to spawn to substrate.