How do submarines like the USS North Carolina-SSN 777 generate and use nuclear energy?

Phenomenon Description: Commissioning ceremony of the USS North Carolina - SSN 777 (US Navy - Virginia Class Attack Submarine) in Wilmington, NC on May 3, 2008. 
Location: New Hanover County, Ocean
Grade Level or Course: Physical Science

Question: How do submarines like the USS North Carolina-SSN 777 generate and use nuclear energy?
Crosscutting Concepts: Energy and Matter: Flows, Cycles & Conservation 
Provide other related questions you considered about the phenomenon.
How can humans live underwater for months on nuclear submarines?
How do nuclear submarines stay under water for months? Interesting Engineering
Science Domain: Physical Science 
NC Standard:
PS.PSc.3 Understand the role of the nucleus in radiation and radioactivity.
NC Objectives:
PS.PSc.3.1 Use models to compare nuclear reactions including alpha decay, beta decay, and gamma decay; nuclear fusion and nuclear fission.
PS.PSc.3.3 Obtain, evaluate, and communicate information to explain the application of nuclear reactions to radioactive dating, medicine, and energy production.

Additional Resources: 
About Nuclear Submarines and Aircraft Carriers, US EPA 
What is Nuclear Energy? U.S. Department of Energy 
How nuclear-powered submarines work and how they compare to other types of submarines | The World - ABC News (Australia) 
Nuclear Reactor Explained GCSE Physics, vt.physics 
Nuclear Fission | Radioactivity | Physics | FuseSchool 
Submarine Nuclear Power | Engineering behind it Nuclear Reactor How it Works |