When we make an animation, Blender makes the interpolation between one keyframe and another with a mode that will make it more or less linear or have special effects...
Video Transcript
When we make an animation, Blender makes the interpolation between one keyframe and another with a mode that will make it more or less linear or have special effects.
This mode can be changed by selecting the keyframe in the Graph Editor window and modifying the Interpolation Type parameter in the F-Curve tab that we can open by pressing the N key.

For example, bezier transitions and those in the Easing group will make smoother transitions than linear transitions, which make more direct transitions instead.
We can also set a default interpolation type for all the keyframes we will create.
To do this, simply open the Preferences window and change the value of the Default Interpolation parameter within the Animation F-Curves section.
