With the capacity for Mutually Assured Destruction still present on both sides, the likelihood of an all-out nuclear strike from either side is rather small. Whatever propaganda on either side is saying, there are hardly any issues between Russia and the US/NATO that can’t be sorted out in a considerably less costly way, through negotiations or conventional proxy conflicts.
But if, against odds, Black Swans arrive and the nuclear option comes to table, we’ll most likely see a carefully scaled conflict. The first shots would be delivering tactical nuclear munitions, in order to measure public and military response from the other side.
Right now, the most likely area for such an exchange seems to be the Baltic Sea nations and the Ukraine. The rationale for that might be Putin testing NATO’s resolve to invoke Article 5 in the face of the imminent threat of nuclear escalation. “Is President Trump willing to sacrifice Pittsburgh for Pärnu?” Most likely, Trump and the Germans would stand down, NATO would collapse, and the prospect of global nuclear war would blow over.