Spawn is the seed material: grain fully covered in mycelium. Use it fresh. Historical publications give age examples, but product, strain, carrier and storage conditions differ. Use traceable supplier guidance and receiving checks; these examples are not a universal expiry rule.
The manual mixes spawn at 2-3 per cent of wet substrate weight; one 300 g bottle serves 10-12 kg of wet straw. The folder says about 100 g per 4 kg wet straw.