In accordance with another question I just put up here :) If you describe something about yourself (age, if you are married), can somebody explain what the appropriate cases are? I know learnt that in the sentence 'Jestem stary' or here, Nasze babcie są stary', stary is acc? While you say 'we are married' (jesteśmy małżeństwa', if I'm right), it is in instrumental? I would love to have an explanation :)
The adjectives depend on gender, number and case.
In singular there are 3 forms for each case. I'll give them in Nominative: stary (masculine), stara (feminine) and stare (neuter).
In plural we split adjectives into 2 groups: masculine-personal (adjectives which are used with masculine nouns naming people) and non-masculine-personal (for the rest of nouns). Again in Nominative: starzy (masculine-personal), stare (non-masculine-personal).
If you use only an adjective, you should use nominative. If you use a noun and an adjective describing it, you should use instrumental for both adjective and noun.
"Jestem stary [Nominative, masculine adjective]"
"Nasze babcie są stare [Nominative, non-masculine-personal adjective]"
"Jesteśmy małżeństwem [noun in Instrumental]"