These two ingredients are used in curries as well as in desserts and beverages. Coconut milk is the liquid squeezed from the grated flesh of mature coconut after the flesh has been soaked in lukewarm water. Coconut cream is a richer version.
To make your own coconut milk, use 3 cups grated coconut to 5 cup water or 2 ¸ cups water to get coconut cream. Soak the coconut in the water for 15 minutes. Mix well with your hand, then tip into a muslin-lined strainer placed over a bowl. Squeeze all the liquid out of the muslin. The operation can be repeated with the already squeeze coconut to produce thinner coconut milk which is acceptable in Tom Kha Soup. However, all this is very time consuming, and removing the flesh from a coconut is very difficult without the right implements.
Fortunately, ready-made coconut milk is available in cans in most places around the world. Stir the contents if coconut milk is required or scoop the cream off the top if you need coconut cream. However, if coconut is totally unavailable, then boiled milk may be used as a substitute.
Please note that coconut milk is not the liquid, which is found inside a fresh young coconut. That water is coconut juice, which is used in mixed tropical drinks, and has none of the properties of coconut milk.