I can relate. I’m just getting into AE. To move frame by frame, use Command + left arrow or right arrow.
To set a keyframe, in the timeline layer list, drill down to the attribute you want to keyframe, say opacity. Click the stopwatch next to it. Change the value and you’ll notice that a yellow marker has been placed in your timeline. Now move to a differnt time and change the value, and another marker will be there.