Solving an NxNxN cube relies on reducing it to a 3x3 state. The generalized method consists of three stages:

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r2 U2 r2 U2 u2 r2 u2 (adjust for cube size)

: This is the universal strategy for larger cubes.

Recommended progression:

For a comprehensive guide on solving any Rubik's cube, the following papers and manuals provide both mathematical theory and step-by-step algorithms: Academic & Technical Papers Algorithms for Solving Rubik's Cubes (arXiv)

Once you have a to a PDF, follow this workflow: