Cilantro has a sweet and citrusy taste. Coriander seed is very widely used all across the Middle East, Central America, and Asia. Fresh seeds (green) are particularly fragrant. Dried cilantro is available but most chefs don't use it as it pales in comparison to fresh herbs which are available in most supermarkets. Its international uses make it a common herb to come by. We see it on top of Vietnamese pho, Mexican tacos, Chinese stir-fries, Indian curries and the like.
Coriander seed is used for all sorts of marinades, brines, dressings, pickles, sauces, spice blends, and pastries. It is a key spice in curries. Besides culinary uses, coriander has medicinal values said to cure certain digestive problems and the essential oil can be used as a topical aid to treat rheumatic pains.
Often with parsley, we pick the leaves for certain dishes and we use the stems for others. With cilantro, it is more common to chop the leaves as well as the stems together. There is a lot of flavour in the stems but just make sure not to use large stems close to the base or they will be stringy.
One little culinary tip to keep in your own compendium is to finish Mediterranean or Middle East dishes with a hit of toasted coriander oil to liven it up. Heat a small amount of neutral oil in a pan, add coriander seeds to toast and release the flavours, then spoon it on a dish just before serving.