Nominative. Genitive. Nominative Plural 
Nominative

The nominative answers the questions who? what?(kes? mis?)

The nominative singular has no case ending.  E.g. See maja on minu oma. Mul on ilus kodu. ´This house is mine. I have a nice home.`

 Genitive or Possessive

The genitive case answers the questions whose? belonging to what? (kelle? mille?) 

The gen. sg. always ends with a vowel. Where the nom. sg. ends with a vowel, the genitive usually uses the same vowel.

Nominative:                  Genitive:
maja "house"                maja
onu  "uncle"                  onu
valge "white"                 white
öö "night"                      öö
kivi "stone"                    kivi

Where the nominative form ends with a consonant, the genitive ends with a, e, i, u.
kolm "three"         kolme
eksam "exam"     eksami
päev "day"           päeva
loeng "lecture"     loengu
õpilane "student" õpilase      nominative -ne > genitive -se
naaber "neighbor"   naabri    nominative -er, -el > -ri, -li
kahvel "fork"        kahvli 
sõber "friend"      sõbra         -er > -ra
poolakas "Polish" poolaka    -kas > -ka

Exceptions:

The genitive case is used for:

1) the attribute preceding the headword to indicate possession, e.g. See on naise auto. ´This is my wife's car.´

2) the object when the activity is completed, e.g. Üliõpilane ostis korteri. ´Student bought an appartement.´

3) the object when the activity is directed to the object as a whole, e.g. Ma võtan toa võtme. Ema ostis poest leiva. ´I will take the house key. Mother bought a bread from the shop. 

The genitive is the word stem which is the base form for all singular cases starting from the illative.

ect. 

 Nominative Plural

The nominative plural answers the questions who? what?

The nominative plural is formed from the stem of the genitive singular by adding the plural marker -d.
tänav, tänava, tänavat > tänavad
naaber, naabri, naabrit > naabrid
nimi, nime, nime > nimed
tund, tunni, tundi > tunnid
kokk, koka, kokka > kokad

E.g. Naine läks ülikooli. Naised läksid ülikooli. ´The woman went to the university. The women went to the university. ´
Päev oli soe. Eestis on päevad tavaliselt jahedad. ´The day was warm. Days are usually cool in Estonia.´