Hi Adrien,

Is this any use to you [ http://anamnese.online.fr/islensk/ ]? Here
are a few English sites which you might already know about:

http://teaching.arts.usyd.edu.au/english/2000/icel/
http://www.utexas.edu/cola/depts/lrc/eieol/norol-TC-X.html
http://www.gutenberg.org/etext/5424

There's also a German introduction to Old Norse online here [
http://www2.rz.hu-berlin.de/bragi/b4/b4fornislenskukver_de_hr.pdf ].

> So... How should I write
> "Mary's dress"
> and
> "Kingdom of France"
> for example ?

"Mary's dress" - 'kyrtill Maríu'. I think this is the most normal
order in Old Norse prose, but 'Maríu kyrtill' is also possible.

"(Kingdom of) France" - 'Frakkaríki' or 'Frakkaveldi'. Both of these
mean literally "realm of the Franks/French". But I think the word
'Frakkland' is more common in the sagas.

> No need to translate Mary, dress, kingdom and France, of course. Any
> word is okay. What I really need is to learn how works the posssessive
> form.

There is no one possessive (=genitive) form which will work with all
nouns. Each Old Norse noun belongs to one of several classes, and
each class of nouns has its own set of inflections.

hnefar Þórs "Thor's fists"
bróðir Auðbjarnar "the brother of Auðbjörn"
Hann er sonr Loka ok Angrboðu "He is the son of Loki and (of) Angrboða"

Hvernig skal kenna Baldr? Svá, at kalla hann son Óðins ok Friggjar,
ver Nönnu, faðir Forseta, eigandi Hringhorna ok Draupnis, dólgr Haðar,
Heljar sinni, Gráta-goð.

How should Baldr be described in kennings? By calling him the son of
Óðinn and Frigg, the husband of Nanna, the father of Forseti, owner of
Hringhorni and Draupnir, enemy of Höðr, Hel's companion, god of weeping.

Notice that some nouns change just their endings, others also change
the root vowel (Nanna : Nönnu). Where the two nouns form a close
compound, the genitive/possessive noun comes first, as in
'Frakkaríki'. Hope that helps! I guess you might have to know some
grammar after all...

LN