Thank you for your really fast answer, I appreciate it. Is there a general rule one could follow or every verb has it own conjugation? For example, in my language (italian) you can guess how to make an imperative sentence by knowing which one of 3 conjugations the verb belongs to.
Regarding number of Polish conjugation patterns you can check https://www.duolingo.com/comment/13589661
I think http://www.skwierzyna.net/polishgrammar.pdf is very good in teaching Polish verbs easy way.
It says (on page 47 of the file)
> The imperative or command form of the verb is usually equivalent to the stem of the 3rd pers. sg. present tense form of the verb, obtained by dropping -e, -ie, -y, -i, or by adding j to -a:
As I remember there are slightly different rules. You also need to know the conjugation
For this kind of verbs (they have -ę ending in the first person singular) you take the form of the third person singular and drop the ending: pisać - on PISZe - pisz! brać - on BIERZe - bierz! For verbs of another conjugation (they have -m ending in the first person singular) you should take the third person plural form and drop the ending: pomagać - oni POMAGAJą- pomagaj! słuchać - oni SŁUCHAJą - słuchaj!
If you want to make a plural form, just add -cie: piszcie, bierzcie, słuchajcie, etc.