Nouns refer to people, places, animals, objects and concepts.
In Italian, all nouns have a gender (masculine or feminine) and a number (singular or plural).
In most cases, you can recognise a noun’s gender and number by its ending.
The majority of nouns ending in -O are masculine (and the plural is in -I), while the majority of nouns ending in -A are feminine (and the plural is in -E).
But there are exceptions to this rule. Moreover, nouns ending in -E can be both masculine or feminine.
If present, you can recognize a noun’s gender and number by the preceeding article. When in doubt, you can look up in a dictionary.