All of the three declensions have both masculine and feminine endings. Compared to the endings of nouns, these ones are an easy deal. Additionaly, the endings of adjectives look very similar to those of nouns, so when you are learning, do compare them.

Note that you can match any nouns with any adjective, meaning that a noun of the first declension easily matches with an adjective of, say, the second declension.

First declension

Masculine examples: baltas, balti (white); žalias, žali (green); didelis, dideli (big); mažas, maži (small).
Feminine examples: balta, baltos (white); žalia, žalios (green); didelė, didelės (big); maža, mažos (small).

Second declension

Masculine examples: gražus, gražūs (nice); sunkus, sunkūs (heavy); bjaurus, bjaurūs (ugly); pigus, pigūs (cheap).
Feminine examples: graži, gražios (nice); sunki, sunkios (heavy); bjauri, bjaurios (ugly); pigi, pigios (cheap).

Those cases that have a palatalizing (softening) letter i (-io, -iam, -ių, etc) change d into dž and t into č. For example, nuoširdus (sincere) changes into nuoširdžiam, nuoširdžiu, nuoširdžiame, nuoširdžių, etc. And nuoširdi changes into nuoširdžios, nuoširdžiai, etc.

Third declension

These adjectives are usually made of other parts of speech and often have a suffix -inis. For example, if you take a random noun like 'protas' (brain), you can make it into a third declension adjective 'protinis' by adding the suffix -inis. Protinis would mean 'of or belonging to brain'. For example, 'protinis darbas' means the work that is being done using your head.

The adjectives of this declension are prone to become nouns. For example, 'stiklinis/stiklinė' (adjective) means 'made of glass', whereas 'stiklinė' (noun) means a glass from which you drink lemonade.

What is more, just like nouns, you cannot form adverbs out of these adjectives, nor can you compare these adjectives. Also you cannot make pronominal adjectives nor the neuter gender out of them. We'll talk more about comparison, pronominal adjectives and neuter gender in the next pages.

Masculine examples: oranžinis, oranžiniai (orange); kompiuterinis, kompiuteriniai (of or belonging to computer); pernykštis, pernykščiai (last year's).
Feminine examples: oranžinė, oranžinės (orange); kompiuterinė, kompiuterinės (of or belonging to computer); pernykštė, pernykštės (last year's).

Those cases that have a palatalizing (softening) letter i (-io, -iam, -ių, etc) change d into dž and t into č. For example, pirmykštis (primitive) changes into pirmykščiam, pirmykščiu, pirmykščiame, pirmykščių, etc. And pirmykštė changes into pirmykščių.

Now that you know the ways of Lithuanian adjectives, you may want to find out how to compare them. After that you will meet the pronominal adjectives and the neuter gender.