this is too vague to answer sorry.

It looks flat and green, usually, but can come in red / black / gold / white variants. It is the plant's method of catching energy from the sun and using it to turn simple molecules into more complex ones to enable it to grow.

Foliage is the collective term for the leaves of the plant. As Beattie says, it is usually green, but can be many different colors. It also comes in many different shapes--not all of them flat, such as pine needles, or the plump leaves of many succulents. By the way, is this a school problem?