Well, it's supposedly about Stenka Razin, the Cossack rebel, but it could be about anyone.
This is a poor translation, I'll try and find a better one.

Oh, it wasn't the evening, wasn't the evening...
oh, I slept so little,
I slept so little,
oh, a dream appeared.

In the dream,
it was as if my raven-black steed
ceased playing, ceased prancing,
yes, he wailed over me.

Oh, the cruel winds flew down,
from the east,
they snatched the dark cap
from off my mighty head.

The Esaul (at the time the Cossack leader's right hand man but now a rank equal to lieutenant) was clever (dogadlyv doesn't quite translate),
he knew how to interpret my dream.
oh, he said,
you are bound to lose your mighty head.

Oh, it wasn't the evening, wasn't the evening...
oh, I slept so little,
I slept so little,
oh, a dream appeared.