Put simply, adjectives are describing words; they tell us something about the subject or object of a sentence (which are usually nouns). They are a very common component of language, and come up in conversation very regularly. Many learners of Polish will wait to start learning adjectives until they have a good base of noun vocabulary, but this can hinder your ability to talk with flow and dynamism, not to mention your ability to convey exactly what it is you want to say. So, before you start memorising and using adjectives in Polish, it's a good idea to get used to the grammatical rules that surround their use, and to be aware of how, like many words in Polish, they will change with usage.
Unlike in English, adjectives in Polish must always agree with the gender of the noun they are used to describe. This agreement of gender is signified by using a particular ending specific to masculine, feminine or neuter nouns, and it is relatively easy to get the hang of. What you must remember however, is that looming like sceptre over every aspect of Polish language is the grammatical cases, demanding, in turn, their own ending changes for nouns and adjectives, which means there is a whole flurry of endings you will have to acquaint yourself with if you're going to use adjectives correctly.
That said, it's not worth getting too worried about. The Polish case system is not as daunting as it first may seem (honestly!). A few select cases (notably the accusative and genitive) will be used much more frequently than others, so getting used to adjective conjugations in these will usually go a lot further.
So, as we have said, even in the nominative, adjectives require specific endings that will mean they 'agree' with the gender of the noun they describe. Strictly speaking adjectives have no 'innate gender', but for the sake of learning, we can refer to adjectives that agree to a masculine noun as 'masculine adjectives', ones that agree to a feminine noun as ‘feminine adjectives’, and so on and so forth.
When you approach adjective conjugations in any case (even the nominative), you will have to know how to be able to identify noun genders, so make sure you're able to do this before learning the rules below. What's more, case changes for adjectives, just like for nouns, go from the stem of the adjective, so you'll also need to be confident in working with adjectives having removed previously associated case and gender specific endings. One last point of note is, as with most conjugations in Polish, there are different endings for singular and plural instances, and sometimes a separate associated ending for masculine personal adjectives (adjectives that describe animate or human masculine nouns). This means there can be up to seven different ones to learn in each case! The rules for adjective endings in the nominative are as follows :
For masculine adjectives, the ending -y is required: dobry hotel (good hotel)
For masculine personal adjectives, the ending -y is required: dobry mężczyzna (good man)
For femenine adjectives, the ending -a is required: dobra dziewczynka (good girl)
For nueter adjectives, the ending -e is required: dobre dziecko (good child)
For masculine adjectives, the ending -e is required: dobre hotele (good hotels)
For masculine personal adjectives, the ending -zy is required: dobrzy mężczyźni (good men)
For femenine adjectives, the ending -e is required: dobre dziewczynki (good girls)
For nueter adjectives, the ending -e is required: dobre dzieci (good children)