Upside down curve in graph editor

You are looking at the speed graph. It shows you the speed between keyframes and also the direction. A rising curve indicates an acceleration a descending curve indicates deceleration. Zero is no movement. When you separate dimensions, the speed graph also indicates direction. Positive values indicate the values are increasing, and negative numbers are decreasing. 

I almost never separate dimensions because you lose the ability to see and edit a motion path with the pen tool. Position values are almost never edited using the value graph because it's impossible to visualize the motion path in the graph. Easing or acceleration changes are much easier for me to understand if I do not separate dimensions.  

A bouncing ball constantly accelerates during the fall, which would be a rising curve, then instantly changes to a decelerating curve when it hits the ground. That gives you a speed graph that looks like the acceleration and deceleration you would expect to see. When you separate dimensions, you get two rising acceleration graphs that are split by a vertical cliff when the ball hits the ground. It's a little harder to see and adjust.

Acceleration on Earth is 32 feet per second per second or (32.1740 ft/s²). When you are working in the graph editor, you can drag the influence handles left or right to get the graphs to look right, but the easiest thing to do for a bouncing ball is to edit Keyframe Velocity (Right click on a keyframe or Shift + Ctrl/Cmnd + k) for the three keyframes. Velocity starts at zero when the ball is at the top of its path and when it is at the bottom of the path. To create a good-looking acceleration curve, an Influence value of about 70% gives you a very nice starting point. As long as these values match and the keyframes at the bottom of the path have the Influence set to Zero, you'll have a realistically looking bouncing ball and a perfect speed graph. 

You can do it all by just dragging handles, and if you click and wait for a while with the default preferences, you can see those values, but for me, it's easier to just set the Keyframe Velocity for anything that I need to bounce by editing the values in the Keyframe Velocity Panel. 

If you need to be scientifically accurate, you could do the math and calculate the precise acceleration curve, and then calculate the difference in time between Earth, Moon, and Jupiter's gravity and create a perfectly accurate ball-dropping and bouncing animation created with keyframes, but it would be easier to make the fall and bounce accurately by using Dan Ebberts wonder full Bounce and Overshoot expressions that I have used in about 50 custom animation presets I have created for creating Dynamic Graphics and Text animations for Explainer videos.

I hope this helps get you started on the proper use of the graph editor. You might also like this tutorial I created a few years ago. It demonstrates using the graph editor and the pen tools to create fully customizable animations. 

You got lucky. I'm working on a whole new tutorial series, and your question let me preview some of my projects. I hope this helps.  In the future, when you have having any issues with a tutorial, please post a link to the tutorial so we can help you figure out the problems. Most of the ones you find on a simple search are created by enthusiasts, and the explanations and even the workflows can be lacking.

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Additional information - i am attempting a bouncing ball animation and was instructed to seperate to X and Y dimensions in P/position. The next instruction was to create position keyframes up and down and up and down in the exact same places on the composition. I took off the easy ease instruction but this is what it looks like with easy ease in the speed graph

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