How to do transition? effect in animation

[MIN HYUN5C2A]

Hello 

I'm trying to learn animation by myself

but How do you capture moving objects or animals (as in the video below) 

in one drawing? ( Sorry for my confusing explanation)

like going from down to up or left to right, like when change directions in one image? 

Here's an example. 

like this from 0:25-0:30 seconds

where the bird is from from the sky to the ground. 

https://www.youtube.com/watch?v=_Ir0Mc6Qilo

I'm just trying to learn basic animation by myself. and 

I'd really appreciate if you could explain in detail as much as possible.

[Rick Gerard]

The bird isn't one image. The flapping wings require additional images. Then the position and rotation of the bird and the background are animated. 

For this style of animation, I suggest that you start with Adobe Character Animator. It is a lot more efficient for this kind of 2D character animation than working directly in After Effects.