Icelandic nouns have four cases. Finding the correct form of the word is called declension. This is a simple declension table for the word lamb:
Nom.lamb
Acc.lamb
Dat.lambi
Gen.lambs
Nobody actually remembers this table by heart, instead people construct some sentence where only a particular case can fit, and see what their own sense of the language tells them.
The helper sentences you use for this are:
  • hér er = here is. This sentence will always need a word in the nominative case (the first case).
  • um = about. This word will always need a word in the accusative case (the second case).
  • frá = from. This word will always need a word in the dative case (the third case).
  • til = to. This word will always need a word in the genitive case (the fourth case).
And since the declension table is always shown in the same order, we fill in our table like so:
Nom.hér er lamb
Acc.um lamb
Dat.frá lambi
Gen.til lambs
When declining words that are plural, you switch “hér er” out with “hér eru”:
Nom.hér eru lömb
Acc.um lömb
Dat.frá lömbum
Gen.til lamba

See also