The software development lifecycle (SDLC) involves 8 stages: 1) determine scope, 2) gather requirements, 3) write specifications, 4) design solution, 5) code design, 6) test program, 7) write documentation, and 8) review and maintain. The stages ensure a systematic process of planning, developing, testing and documenting a software project. Requirements gathering is critical to understand user needs, while testing verifies the program functions as intended. Documentation provides instructions to users and information for future maintenance.