Both the leaves and seeds of coriander are used in Mexican cooking.
The plant closely resembles flat leafed or italian parsley in appearance but the flavor is much stronger and distinctive. The leaves of the plant are usually chopped up and added to salsas or sprinkled on tacos.
There seems to be no middle ground for this herb - people either like it or they don't. I have one friend who describes it as tasting like moldy socks while I can't imagine eating without it.
Purchase plants that look healthy and have no dead leaves. You can remove the leaves from the stem and store them in an airtight container n the fridge or, if you aren't feeling quite so ambitious, place the plants in a glass of water also in the refrigerator. Either way, the cilantro should remain fresh for up to a week.