look for 'intensity' on he channel box, (redline) press on it so it goes black(the node n the channel box) like in the picture, (red line) then right click and press'key selected.'

middle mouse button on the time line where you want to set your next key, change the intensity in the channel box, right click again and pick 'key selected' again.

thats it, you can do that for rotate or any other thing you want to animate, translation, rotation, anything

I hope this is what you mean