Google App Engine is a fully managed, serverless platform, developed by Google, which would help you in developing and hosting web applications, in Google’s data centers. This Platform-as-a-Service (PaaS) offers you with a huge set of libraries, languages, frameworks, that are needed to develop an app. And once you develop the app, you could leave it to Google App Engine or simple App Engine that will take care of your app instances and scale that based on demand.
If you wish to advance in Google Cloud Platform, I would recommend you to take up the GCP certification course, from Intellipaat, which would offer you dedicated instructor-led training and guided projects that would help you in developing practical skills. I would like you to watch our YouTube video on Google Cloud Interview Questions and check out the GCP interview questions to ace the GCP interview.