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

Phenomenon Description: The USS North Carolina - SSN 777 (US Navy - Virginia Class Attack Submarine) uses nuclear energy. 
Location: N/A
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?
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 | 
Image: https://www.dvidshub.net/image/88092/commissioning-uss-north-carolina 
Commissioning ceremony of the USS North Carolina - SSN 777 (US Navy - Virginia Class Attack Submarine) in Wilmington, NC on May 3, 2008.