i have just bought a zantedeschia plant what are the care instructions?

Depends which one - if its Zantedeschia aeothipica or a variety of that, it likes damp soil (can also be grown in water, like a pond) and will withstand several degrees of frost. Other forms of Zantesdeschia (usually with spotted leaves) are tender, can can be stood outside in summer, but are not frost hardy, nor do they require the same level of dampness in their soil.