Seeds house and protect the tiny plant embryo produced during fertilisation. They also contain nutrient stores (endosperm) that provide energy to power the stages of germination, before the plant is able to begin photosynthesising and producing it's own food.
In the spermatophytes or seed bearing plants seeds aid in dispersal and in colonisation of harsh terrains. The endosperm and protective seed coat (testa) allow the seed to remain dormant until conditions are favourable for germination.