Travis CI is used by Sentry to automate testing and view results within pull requests, allowing for the creation of Sentry Releases that enable features like identifying commits that likely introduced new errors. A .travis.yml file is used to configure Travis CI, including setting programming languages and version numbers, as well as customizing the build process with hooks. To create a new Sentry Release, environment variables are set using `env` in the `.travis.yml` file, and the Sentry CLI is used to install and finalize releases after the build phase completes successfully. The complete `.travis.yml` file for this example includes scripts to run tests, create a new Sentry release on push to master, and use the Sentry CLI to finalize the release.