# Why does blender erase transforms after inserting a keyframe?

I have a default cube. I would like to animate it. For example I would like to make it rotate around the Y axis. I add a rotation keyframe (I) at frame 0 and at the last frame I add another rotation keyframe. Then, I set the yellow Transform Rotation Y field to 180°.

And instantly, 180° rotation disappears and no rotation occurs when playing animation. Why does Blender erase the keyframe settings? And how should I make this work properly?

In fact, I am trying to go trough this tutorial and my object doesn't behave in the mentioned way. When I move/rotate/scale my cube, the F-Curves are not updated. What I might be doing wrong?

The keyframe is updated with the current value at the moment you press I or insert the keyframe. After that, the value will not be (permanently) modified any more until you press I again on that exact keyframe.
So if you press I and rotate afterwards, that rotation has no (permanent) effect and is lost as soon as you leave the keyframe. You should rotate first and insert the keyframe afterwards, or at least press I again after rotating, basically to save the modification to the keyframe.
You can insert new keyframes by pressing I on the 3D View and selecting the properties in the popup menu, pressing I on any numeric field in Blender (whether transforms or modifiers/material/constraints properties) or by right-clicking on any field and pressing Insert Keyframes (or Insert Single Keyframe).