You use adjectives to describe objects or people, la chaqueta grandethe large jacket.
Spanish adjectives have different endings depending on what they're describing.
With masculine nouns, adjectives end with -o, while for feminine nouns they end with -a.
El sombrero rojoThe red hat
La camiseta rojaThe red top/tee-shirt
Others like grandebig and azulblue stay the same:
El sombrero grandeThe big hat
La falda azulThe blue skirt
When describing more than one thing, you add either an -s, when the adjective ends in a vowel, or -es, when it ends in a consonant.