1) When you create position keyframes for something like this, Motion creates "smooth" animation (Bezier points). It used to create linear keyframes, but a lot of people wanted "smoothing" by default, and so Motion tries to figure out what you're going for... with smoothing. A lot of times, it will depend on *how* you create your keyframes as to what Motion will make of them.
2) when you right click on any Position parameter and Show in Keyframe Editor, you get 3 paths (X, Y and Z). You can turn off the visibility of the X and Z "curves" by unchecking them in the set list on the left side so you can focus on just a single keyframe set at a time in the editor,
One way to control how Motion creates a keyframed animation like yours is to set up the text where you want it to pause. Set all 4 keyframes with the text in place, then move the playhead to the first keyframe and change the Y parameter down; then go to the last keyframe and change the Y parameter up. What Motion will do is create keyframe interpolation like this:
[Note: when you create more than one keyframe for a parameter, two arrows to the left of the yellow/orange diamond *may* appear [depending on the existence of previous and next keyframes]. These are button shortcuts for "go to previous keyframe" and "go to next keyframe". This is the fastest, most accurate way to position the playhead on those keyframes.]
The first keyframe has an ease out. The 2nd keyframe is a Bezier curve but with the keyframe point "split" (or broken) — the first half of which will behave more linearly than accelerate in (because it's rather gradual). You can see the "outgoing" handle to the right of the 2nd keyframe and the ingoing handle of the 3rd keyframe **on the line** between the two making the "interpolation" a linear one. The outgoing handle on the 3rd keyframe creates an "ease out" (which is typically what you would want) and the last keyframe is set as an "ease in". All in all - it's a fairly smart "guess" by Motion.
By setting up your keyframing in this fashion, you're basically creating a straight-line animation to start, then "breaking" the first and last points away from that line. The "line" in between (keyframes 2 and 3) usually has its linearity preserved.
At this point, in the Editor, if you want to change the 2nd keyframe to have an Ease In effect, you will notice that there is no in-going "handle" to change. Hold down the Command key and click on the keyframe and drag out of it to get the left side handle. You can use the shift key to constrain the handles to 0, 45, 90, 135, 180º, etc. angle, which is most helpful when you need to maintain that linearity you have between keyframe 2 and 3.
You have to be careful clicking directly on keyframe points as they may shift their position. I usually recommend selecting by dragging a selection rectangle around them.
As with all things Motion, there are usually more than one way to handle things. Hang in there. All in all, Motion is really easy to use... most of the time... ;) And: we're here to help!
