It’s not just numbers. Almost all verbs are like that.
Say “jumping” - skakać
I am jumping - skaczę I was jumping (male) - skakałem I was jumping (female) - skakałam you are jumping (singular) - skaczesz you were jumping (singular male) - skakałeś you were jumping (singular female) - skakałaś you are jumping (plural) - skaczecie you were jumping (plural male) - skakaliście you were jumping (plural female) - skakałyście they are jumping - skaczą they were jumping (male) - skakali they were jumping (female) - skakały
And so on and so on. You have no chance of remembering all of that - you either learn the rules and how to apply them, or you fail at polish language
You mean declension - yeah, there are seven. For every single noun.