subject + verb (+object)
Subject is always in nominative case and object is a) in partitive case, if it's uncoutable or an abstract entity b) in genitive case, if countable. In negative sentence c) object is in partitive case. Because ei is verb, it conjugates in person. The other verb is without any endings (the stem).
This is the most prototypical sentence, wich can be used in various situations.
subject + kopula + predicative
Subject is always in nominative case. In singular form object is a) in nominative case or b) or in partitive case, if it's a mass noun. (usually, something is made of something.) NB! In plural form must be used partitive case. Right: Suomalaiset ovat hiljaisia. Wrong: ?Suomalaiset ovat hiljaiset. Negative sentence is formed similar to verb sentence, but the predicative is in same case as in affirmative sentence. The stem of olla is ole.
Kopula sentence can be used to describe things or to express similarities between the subject and the predicative.
locative + verb + subject
Lokative is always in inessive tai adessive case.
Verbs is always on.
Subject is a) in nominative case or b) in partitive case, if it's indefinite.
In negative sentence d) subject is in partitive case. The stem of olla is ole.
Existential sentence can be used to express where things are (or are not) or possession.