Use the code in this Github repository with the provided directions to deploy a functioning web application to control supported Nest devices such as cameras, doorbells, and thermostats. You'll need your Google account credentials and a Firebase project.
You can try out a live demo at https://device-access-sample.web.app.
If you are new to Device Access, we recommend you start with the Building a Device Access Web Application Codelab prior to using the Web Application Sample.