Fastlane is an automation tool that makes building, testing, and uploading apps effortless for iOS and Android platforms. It offers portability, allowing users to run it on other developers' machines and the cloud. The process starts with setting up prerequisites such as App Store Connect API key and GitHub repository, then initializing fastlane with `fastlane init`. Users can modify the generated Fastfile to suit their needs, including adding a new lane for testing and uploading to TestFlight. The setup includes code signing using Match, which maintains certificates and profiles for easy consistency across machines. The final step is to run the beta lane, which signs, builds, tests, and uploads the app to TestFlight, with options to check in version number changes and tag builds.