Seeds are an item used in farming. They can be found by tilling grass tiles with a hoe to make farmland or by harvesting fully-grown wheat. The chance of finding seeds while tilling is fairly small compared to harvesting wheat, which yields from 0 to 3 seeds per tile harvested. Seeds can be placed in farmland by right-clicking, where they will grow.
Growth
When left alone, seeds planted in farmland will grow to become wheat which can be harvested. Planted seeds need at least 1 block of air above them to grow, and grow more quickly when planted near abundant water and sufficient light. The image below shows the stages of growth from newly planted seeds to wheat that is ready for harvesting. Allegedly, as of Beta 1.2_02, when harvesting fully matured wheat, there's a chance of it not dropping wheat.