There are two main types of adjectives in Spanish:
1. Four-form adjectives that end in "o" and agree in gender and number.
2. Two-form adjectives that end in "e", consonants, or "ista" and agree in number only.
There are some exceptions - adjectives of nationality and those ending in "ón", "án", "ín", or "dor" are irregular and have four forms even if they end in consonants. Descriptive adjectives generally follow the nouns they modify.