It means that you need to learn every verb kind of ..... twice!
For example: two forms of the verb 'cook' are 'gotować' and 'ugotować'.
The imperfective- you can use when you speak about the present, the past and the future.
The perfective- you use when you speak about the past or the future.
So, when you speak about the present, you dont have to decide which form to use (always imperfective), but when you speak about the past or the future you should think if you need the imperfective or perfective form.
The imprefective form is used when speaking about continuous, repeated or lasting actions.
The perfective form is used when speaking about single, complete actions.
The imperfective form is more like: I was cooking the lunch for 2 hours (lasting) or: When I was ill, I was cooking lunch everyday. (repeated). I compare it with Past Continuous in English.
The perfective form is more like: I cooked lunch yesterday. (one single action). I compare it with Past Simple in English.
The imperfective form is the basic one and you can find it in each dictionary. Unfortunaetly there are no rules how to make the perfective one. However, we usually add prefixes at the beginning:
to call: dzwonić (imperfective)- zadzwonić (perfective)
to write: pisać- napisać
to do: robić- zrobić
to wait: czekać- poczekać
As you see, prefixes are really diffrent, so you just need to learn it by heart.
In some verbs, the change is in the infinitive ending, or within the stem itself:
to borrow/ to lend: pożyczać/ pożyczyć
to order: zamawiać- zamówić
to speak- mówić- powiedzieć
THE LIST OF A FEW MORE
IMPERFECTIVE AND PERFECTIVE FORMS:
to eat: jeść- zjeść
to drink: pić- wypić
to pay: płacić- zapłacić
to watch: oglądać- obejrzeć
to meet: spotykać się- spotkać się
to call: dzwonić- zadzwonić
to go: iść- pójść
That is enough for today, we will continue this topic soon :) I will prepare some exercises to practise as well!