Use your arrow keys to navigate to the next and previous frames. If you're on a mobile device, swipe left and right.
Squash and stretch is easily seen with a ball bouncing. In animation, it's important to exaggerate your drawings-- and when working at many frames per second (12, or even 24 for film), it's typical to draw in frames that you will "feel" and not "see".
In the case of a bouncing ball, or Flippy the frog, SQUASH happens at frame 7. Pause the above animation and navigate to that frame, then compare to frames 6 and 8. Wow, what a difference! 6 and 8 are squashed frames. Contrasting squash and stretch makes the animation exciting to watch.
Not all things need to be as simple as a ball. If stand up to jump, you'll find that your whole body "squashes" a little when you land (bending your knees, and probably bending your spine a little). You will "stretch" when you're in mid-jump, where your legs and spine (perhaps even arms) straighten out!
Muscles squash and stretch too!