Adjectives in Polish decline, and agree in gender and number with the noun being described. Your task is to learn how to do this, or at least to recognise what is going on.
Now grammar isn't popular (I wonder why?), and many people are scathing about studying grammar.
The usual reasons given are it is boring, you can't learn it all, (I have a Polish grammar with over 600 pages, and sympathise with this view) or just to gloss over it.
Maybe you can do that with Spanish or other romance languages (I'm not so convinced personally), but if you want to learn a slavic language with a grammar very different to English, grammar is not a subject to ignore.
It won't go away and if you want to construct you own sentences (correctly) then you have to learn or absorb it in some way.
My (partial) solution with Polish (and I am by no means an expert) has been to learn enough grammar to allow me to recognize how a sentence is structured and then read and read and read, to try and assimilate the constructions.
And this table, is my attempt to simplify the horrendously complicated structure so that I can recognise the (majority of adjectival) endings.
This is obviously a massive simplification and I haven't bothered with the Dative, Locative or Vocative cases for various reasons which I won't bore you with here.
The above should be sufficient to in the many cases to understand adjectival agreements used in the sample sentences (or anywhere else for that matter).
Maybe this will help someone. Maybe it won't.
But even if it doesn't at least I won't misplace this handy table, where I have condensed at least one hundred pages from Polish. A comprehensive grammar, into one easy table ;)