This is the 287th most frequent Czech word.
stalo
"Stalo" in Czech means "happened" or "occurred" in English.
In this sentence, 'stalo' is used as the past-tense form of 'stát se', meaning 'to happen'. It asks about a past event.
Co se tady stalo?
What happened here?
Here, 'stalo' again refers to the past event as the occurrence in question occurred the previous night.
To se stalo včera v noci.
This happened last night.
In this statement, 'staly' is used as 'stalo' in plural form to refer to events happening multiple times in the past.