This will download the [Nightly version](https://github.com/keycloak/keycloak/releases/tag/nightly) of the Keycloak server and run it locally on port `8180`. If a previously downloaded version was found in the `server/` directory then that one will be used instead. If you want to download the latest Nightly version you can remove the server directory before running the command to start the server.
In order for the development version of the Admin UI to work you will have to import a custom client to the Keycloak server. This is only required during development as the development server for the Admin UI runs on a different port. This client will be imported automatically under the name `security-admin-console-v2` when the Keycloak server starts.