How Nuclear Bombs Work
The recent film Oppenheimer portrays the human and societal impacts of nuclear weapons while avoiding any technical depth. If you are interested in the scientific side of this story and how these lethal devices are designed, the Belfer Center online lectures are a great source of information.
Beyond the topic of bomb designs, the discussion on enrichment techniques is of particular interest and relevance in the context of international policies. We learn about the difficulties in producing weapons grade material and how this forms a bottleneck in access to nuclear weapons.
Watch: How Nuclear Bombs Work - Part 1 :: 1h6m
Watch: How Nuclear Bombs Work - Part 2 :: 0h45m
To get an idea of how deadly these weapons are, the following tool shows the blast radius of various real-world nuclear weapons:
Try: NUKEMAP by Alex Wellerstein
As for the range of current weapons, the MISSILEMAP tool contains a list of known launch sites and their possible targets: