There are 15 cases in Finnish: a group of common cases, a group of six local or locative cases, and a group of relatively uncommon cases.
Arguably, the most important case for Finnish-language learner is the nominative (Finnish: nominatiivi). It is the "dictionary" case; a word in this form can be found in the dictionary. If a word is in another case, you need to change it to its singular nominative form to be able to look it up in a paper dictionary. Online dictionaries offer suggestions that make looking up words in a dictionary easier.
Finnish cases coincide with some English prepositions, such as inside, on, and from. In Finnish, cases have case endings (suffixes). As it sounds, you attach cases to the ends of words.