Walking is a metaphor for living. Alternate translation: "conduct your life in the power of the Holy Spirit" or "live your life in dependence on the Spirit" (See: [[rc://en/ta/man/jit/figs-metaphor]])
The word "flesh" here is a metonym for the sinful nature and is spoken of as if it were a person and wanted to sin. Alternate translation: "what you want to do because of your sinful nature" or "the things you want to do because you are sinful" (See: [[rc://en/ta/man/jit/figs-personification]] and [[rc://en/ta/man/jit/figs-metonymy]])