1st GROUP

They are declined using the ends of the first and second declensions. Using the second declension for masculine and neuter, and the first for feminine.

2nd GROUP

They are declined using the ends of the third declension. Depending on the ending they have  in the nominative singular form, they are grouped into:

• Adjectives of one ending: just have one form in the nominative singular masculine, feminine and neuter. In this case its statement is the same as for nouns (nominative and genitive), but with the difference that you do not give any kind of gender, as the adjectives lack it.  Ex.: ingens, -NTIS
• Adjectives of two endings: in the nominative singular form have a termination for masculine and feminine, and another one for the neutral. Ex.: fortis, -E
• Adjectives of three endings: in the nominative singular form, they have a termination for each gender. Ex.: acer, acris, acre

The distinction between adjectives of one, two or three endings is not very relevant, since, except the nominative singular, the rest of the decline is identical: