understandI understand why he did that.
comprehendHe doesn't seem to comprehend the scale of the problem.
get the pictureinformalOK. Don't say any more. I get the picture.
followIt was so complicated I couldn't follow what he was saying.
graspI think I grasped the main points of the lecture.
fathomUKFor years, people have been trying to fathom the mysteries of the whale's song.
getI told him a joke, but he didn't get it.