Did the Russians really hack the 2016 elections? If they did what did they really hack?

What systems did they hack into? Democratic National Committee websites?  Mr. Podesta?

And now we hear President Obama stating that the US will now retaliate against Russia for their apparent involvement. As was stated once before President Obama stated the US would retaliate.   What sorts of actions would be expected in a retaliation against the Russians? We have heard that the US intelligence CIA NSA already has access to the Russian power grid and much more, while there are many ways the US could retaliate perhaps in ways we may not even notice.

Now we read that China has stolen a US underwater drone, captured in disputed waters.  This could potentially escalate an already tense situation.  Is the US position to retaliate against China for this?