How to add or remove keyframes in Premiere Pro?

Click on the Toggle Animation and change parameters of some property such as Position, for example. Wherever you see a Toggle Animation means that you can do animation.

Keyframes are added by enabling keyframing and then changing the property at a different time in the timeline. Time remapping is used to change the timing of video playback. A time remapping keyframe is a specific point in time so you if you want to move that point in time you just set a keyframe or multiple keyframes and drag them around the timeline. It takes a few minutes to wrap your head around manipulating time so be patient.

These are extremely basic tasks. Make sure you are familiar with the User Guide and the basics of the UI. Just asking questions on forums is a pretty inefficient way to learn an app as complex as After Effects. I could run college-level classes for a couple of years and still just touch the surface of what AE is capable of.