Lock screen in Android

I see a lot of posts about lock screens and app to show something on it.

In Windows I can lock my screen with Win-key + L. Windows shows a rather empty screen, so I need to do a mouse click and enter my password, just as when it’s booted. I never do that, because I use hibernate in such cases, a feature that Android doesn’t seem to have.

How do I lock an Android phone or tablet to be sure nobody else uses it? And what does it show then by default? Closing the case might work, but then it would be useless to use an app to show something on it. So I assume there is another way it can be triggered.