I'm a little bit lost with the cases,
Genetive = undirect object Accusative = direct object Nominative = others? Voccative = imperative?
Have some examples please?
Vocative is the case used when you speaking directly to a person. It's nearly always the same as the nominative, except for most masculine nouns in the singular.
For example, when you call your friend Eleni, you call Ελένη! (same as nominative), but if you call your friend Costas, you call Κώστα! (without the final -s).
Nominative is the basic or dictionary form. It's the case used for the subject of a verb - the person or thing that does the action.
Accusative is the case used for the object of a verb - the person or thing that receives the action, that gets acted on. It's also the case used after many prepositions.
Genitive is the case used for possession, e.g. το βιβλίο του πατέρα "the father's book".
Genitive pronouns are also used for the indirect object -- this used to be dative (as e.g. in German), but Greek lost the dative case centuries ago. But nouns usually don't use the genitive case; instead, you use a preposition + accusative case, as in English: Δίνω το βιβλίο στον πατέρα = I give the book to the father, with preposition σε in Greek and "to" in English.
Here's one with three cases:
Ο πατέρας της δίνει έναν αναπτήρα. "The father gives her a (cigarette) lighter".
Ο πατέρας is in the nominative case because the father is the subject of the sentence - the one doing the giving.
της "(to) her" is in the genitive case, which is used for pronouns representing an indirect object - the recipient of the giving.
έναν αναπτήρα is in the accusative case (nominative would be ένας αναπτήρας) because it is the object - the thing which is given.
If instead you wanted to say "The father gives the woman a lighter", it would be Ο πατέρας δίνει έναν αναπτήρα στη γυναίκα, with στη from σε + τη -- preposition + accusative case.
Κύριε! Πού είναι οι μπλούζες; Τις βάλατε στο κρεβάτι; "Sir! Where are the blouses? Did you put them on the bed?"
This has a vocative κύριε "sir!" from κύριος "sir, mister, lord" used because you are calling the person with that word; a nominative οι μπλούζες (since they are the subject of the second sentence); an accusative τις "them" (feminine plural) because they are the object of "put"; and another accusative with preposition στο κρεβάτι "on(to) the bed".
Ok I understand better than yesterday ^^
But it would be hard to do a right sentence at the begining, I mean I understand your explanations but I don't think that I can tell a right sentence spontaneously.
And there are a lot of different ways to tell the same thing so I think I have to train myself.
Thank you for your help ! :)