Spanish nouns come in two genders, masculine and feminine. The basic rule you can learn is that
masculine nouns end in o and feminine nouns end in a, although there are many
exceptions to this rule. Here are some more common endings that can help you
distinguish between masculine and feminine nouns.
Some Masculine word endings
-o (carro)
-ete (caballete)
-amen (dictamen)
-ista (unless referring to a woman)(el dentista, la dentista)
Some Feminine word endings
-a (carroza)
-ción (canción)
-ía (lotería)
-ez (vejez)
-dad (humildad)
-tud (juventud)
Some common exceptions
el día
la mano
words of greek origin ending in -ma (el poema, el clima, el idioma, el problema, el tema)
Agreement
There should be agreement as far as gender and number when you put nouns and adjectives together.
If I want to say the red house I need to say La casa roja. Now if I want to talk
about more than one house, I say Las casas rojas. The article "La" changed to "Las" to agree
in number with the noun, and the adjective "rojo" did as well. If I want to talk about a red car,
the adjective again must change to agree in both gender and number un carro rojo