They are also called cilantro or Chinese parsley. It can used every parts of it. 

1.  The root has a strongest flavour than another parts.   They are used in curries, soup and curry pastes.

2. The stem  can be used instead of the root. 

3. The leaves are often used in soup, salad, curries and for garnishing. 

4. The seed need to be roasted over a low heat (without oil) until  turn to dark brown colour then it can crunched and pound or blended into powder form it will be ready  used  for making curry pastes and marinade meat for deep fried which can make a nice an aroma.

Fresh coriander can be stored in the refrigerator by wrapping in tissue paper and putting into plastic bag. It will last for a week or it can also be frozen. 

Dried coriander or parsleys can be used as a substitute ( 1 tbs. of dried coriander = 2 tbs. of the fresh coriander )