'can' vs 'could' - ability (umiejetnosc, zdolonosc)
Umiem cos robic = I can do
I can write songs.
Nie umiem czegos robis = I can't do
I can't sing.
Umialam cos robic = I could do
I could walk when I was three.
Nie umialam czegos robic = I couldn't do
I could't read or write until I was six.
Bede umiala cos zrobic = I will be able to do
I will be able to drive a car in a month's time.
Nie bede umiala czegos zrobic = I won't be able to do
I won't be able to speak Spanish in a year.
Moglam (bylam w stanie) cos zrobic = I was able to do/managed to do
I was able/I managed to start my car this morning.
Nie moglam (Nie bylam w stanie) czegos zrobic = I couldn't do/I wasn't able to do/I didn't manage to do
I couldn't open/wasn't able to open/didn't manage to open the door to my house last night.
'can' vs 'could' - ability (moznosc)
Moge cos zrobic = I can do
I can pick you up at the airport later on.
Nie moge czegos zrobic = I can't do
I can't see you tonight.
Bede mogla cos zrobic = I will be able to do
I think I will be able to help you, but only tomorrow.
Nie bede mogla czegos zrobic = I won't be able to do
I won't be able to come to your party, I'm afraid.