Latin genders
Unlike English, Latin nouns have a gender which is either masculine, feminine or neuter.Unsurprisingly, men are masculine and woman are feminine.
However, this doesn't mean that all other nouns are neuter. To be certain of a nouns gender it has be learnt, although it is often possible to deduce the gender from its endings in the nominative and genitive. (If you have learnt these - otherwise you have to guess).
For example, labor (work) and ignis (fire) are masculine nouns while fabula (story) is feminine and mare (sea) is neuter. There is no particular reason for the gender of these nouns.
Rules to help determine Latin gender
There are no absolute rules to do this. However, the following can help
If a noun belongs to the first declension then it almost always has the feminine gender.
If a noun belongs to the second declension, and the nominative singular is -um then its gender is neuter.
If a noun belongs to the second declension, and the nominative singular is -us then its gender is usually masculine.
Fourth declension nouns, ending in -u are all neuter.
Why does the gender of a noun matter?
Because nouns and adjectives 'agree' which means that the ending that an adjective uses will depend on whether the noun is singular or plural and its gender. And so on ...