What the Gulp tasks do: -
1) clean - deletes SharePoint Framework build folders and intermediate Sass files in the src folder
2) build - build the project
3) default - equivalent to bundle
4) bundle - build, localize, and bundle the project
5) dev-deploy - deploy the current project to a development Azure CDN for sharing builds with colleagues
6) deploy-azure-storage - upload the assets to a Azure storage container
7) package-solution - package the project into a SPPKG
8) test - build, localize, and bundle the project and run tests, and verify the coverage
9) serve - build and bundle the project and run the development server
10) trust-dev-cert - generates and trusts a development certificate if one isn't already present
11) untrust-dev-cert - untrusts and deletes the development certificate if it exists