I am relatively new to Blender and am looking for help with my animation. I know all about keyframing but my question is how to make the speed of an object constant when it moves between 2 keyframes, instead of it starting slow, going quickest in the middle, and slowing at the end.
What you're looking at is the default interpolation (that is, the rate things move between keyframes). From your description, it is likely that your default interpolation is set to Bezier, which looks like below:
Get into the Graph Editor, select the channel you want to change (the names next to the eye in the above picture).
Then you want to go to the
Constant. It'll move constantly after that.
You should change the Interpolation Mode. The default is "Ease [in, ease out]." It sounds like you're wanting "Linear."
You can change this in the Graph Editor:
...using this panel:
That panel is also in the first image, it's just empty because there are no keyframes selected.
You don't have to change each keyframe individually. You can select a group of keyframes, or a whole curve, but the point is that the interpolation is on the key, not the curve.
More on F-Curves in the Manual.