In order to use a verb in conditional mood in Polish language, you need to know how to conjugate a verb and add the particle BY before ending in appropriate form:
There are 6 endings of a verb depending on gender and number here: -ł(m), -ła(f), -ło(n), -li(m, pl), ły(f, pl). After these endings you have to add the particle BY in appropriate form: -bym(ja), -byś(ty), -by(on, ona), -byśmy(my), -byście(wy), -by(oni).
For example: Czekać – to wait, JA CZEKA-Ł-BYM – I would wait
Let’s consider how to do it with the verb OTWIERAĆ – to open.
| Ja otwierałbym Ja otwierałabym | I would open |
| Ty otwierałbyś Ty otwierałabyś | You would open |
| On otwierałby Ona otwierałaby | He would open She would open |
| My otwieralibyśmy My otwierałybyśmy | We would open |
| Wy otwieralibyście Wy otwierałybyście | We would open |
| Oni otwieraliby One otwierałyby | They would open |
Examples
Ja mógłbym podreperować ten rower – I would be able to repair this bicycle (reperować/podreperować – to repair, ten – this, rower – bicycle)
Ona nie otworzyłaby drzwi – She would not open the door (drzwi – door)
Pracowałby Pan w banku? – Would you(formal, masculine) work in a bank?
Co Państwo kupowaliby? – What would you(formal, plural, masculine) buy?
Grałbyś z nami? – Would you play with us? (grać/zagrać – to play)
Also, the particle BY is part of the words ABY, ŻEBY – to/in order to; JEŚLIBY, JAKBY, GDYBY – if (would). It means that one will have to use appropriate form of the particle according to the context. In case if you use BY with these words – there will not be the particle BY in end of verb that is after these words. For example:
Abyś robił to, byłbyś bogaty – If you did it, you would be rich. Abyś robiłbyś (bogaty – rich)
Jeśliby oni mi powiedzieli! – If they told me! Jeśliby oni mi powiedzieliby
Gdyby Pani wypróbowała to wino, byłaby zadowolona! – If you(formal, feminine) try this wine, you would be glad! (zadowolon – glad, ta – this(f), probówać/wypróbować – to try)