Memorize the endings below, because these endings form the plural first declension nouns:

Nominative: –ae

Genitive: –ārum

Dative: –īs

Accusative: –ās

Ablative: –īs

Here’s an example of first declension plural endings for the word farmer in Latin.  Even though first declension nouns are usually feminine, the Latin word for farmer is masculine.

N: agricolae

G: agricolārum

D: agricolīs

Acc: agricolās

Abl: agricolīs

The following are the first declension plural endings for trumpet:

N: tubae

G: tubārum

D: tubīs

Acc: tubās

Abl: tubīs

Note: in the plural, the dative and ablative have the same endings.