Card sorting can be used in various ways but the common aspect is that you need a good bunch of people participating, 15-30 depending on your time and topic. The idea is to create cards, with words or drawings and ask participants to cluster them.
You can ask them to rank regarding what they think is the most important to them, or put them in a special situation like "what if you were really rich?" and ask them to cluster the cards.
Card sorting is a good method for interface design, especially to create menus, structure data. You can give cards with all the different headers of your website, electronic device... and ask the participants to cluster them and label each group (Open Card Sort) or give them the group names and ask to put the cards in the group they think corresponds the best (Closed Card Sort).
Cards can also be drawings, in order to be used when verbal communication is complicated.