Obviously, I am completely ignorant about everything to do with nuclear bombs
but I have googled, and my tiny mind just doesn't grasp how this works.
In theory, could the UK/ US/ France/ Germany/ several other countries all suffer hits seconds apart? 
Or would Putin have to choose one to be the first? How would he choose targets?
I understand the idea of mutual assured destruction if there are just two entities battling it out - but I don't understand how the dynamics of MAD work if it is Russia vs numerous countries, and Putin can only target one area at a time?
Is the nuclear capacity at his disposal really so huge he could take out many major cities and all military bases in Europe and the USA all at once?