The new to me Flash

So I win a flash on ebay. Just a sigma, nothing too exciting. That was all the budget allowed.
So far, it seems to be exciting. I can't figure out the metering tho??? Very strange. Pictures are saying that I am very under exposed. But they seem to come out fine. So, I started playing. I found some Xmas decorations in the closet. Set them up on a silver like "white board" that the kids were no longer writing on, and practiced away.

I liked it.