Freshly-ground coriander seeds make excellent powder.
Coriander seeds are generally ground into a powder before using in curries in the same way that one would use coriander powder. It is a staple spice of Indian cooking, and coriander is almost always present in a curry.
One could be forgiven for asking why bother with these seeds, when the powder is available? The reason is that freshly-ground coriander has a more intense flavour... the essential oils within the seeds are volatile, and disspiate quickly. So it is better when freshly ground, even though it is a bit more hassle.
For best results, heat for 1-2 minutes in a pan before grinding, then use immediately. You can use a mortar and pestle to grind it, or a rolling pin, or one of those special blender attachments for grinding spices.