How to "activate" some camera, i.e. view through it? Suppose, I have some camera in the scene and I want to view scene throug this camera. How to do this?
First I read this should be done by Ctrl Numpad 0. It worked once then stopped.
Next I read this can be done via selecting desired camera in Scene panel. This also worked once then stopped.
Here is the UI

As you see, camera si highlighted and also selected in scene pane. Also you see that camera is seen from aside, so we are not viewing through it. Pressing Ctrl-NumPad0 does nothing.
Ctrl+Numpad 0 sets an object as an active camera, but is not intended to change the point of view itself.
In order to view from the active camera, just press Numpad 0 or on the 3D Viewport's menu choose  View&gt; Viewpoint &gt; Camera.
Or select View &gt; Cameras &gt; Active Camera