I know that atleast till the age of one baby's foot goes chill often and we need to socks them ... But I don't know why??? Please share your thoughts or if there is a specific reason to it.

All human beings loose heat from their extremities ie feet and head. In a cold climate even adults use a warm cap and woollen socks. Babies are a little more delicate and hence when the weather is cooler keep their head and feet covered.