First, in this chapter, we'll find plenty of visual imagery. Any time the narrator uses specific words that show us exactly what the objects and characters in the story look like, that's imagery. Here's an example:
The higher slopes grew dark with heather. Patches of rougher and more bristling green appeared in the valley. Digory did not know what they were until one began coming up quite close to him. It was a little, spiky thing that threw out dozens of arms and covered these arms with green and grew larger at the rate of about an inch every two seconds.
Above, notice that the narrator didn't vaguely state something like "There were trees around Digory." Instead, he showed the precise color and shape of the trees so that we could envision them in our minds.
Second, Uncle Andrew's outburst is full of hyperbole, or exaggeration for effect. He uses extreme language to express his anger and frustration; as a result, we can sympathize with him and understand that he might be going a bit crazy. The hyperbole also simply makes this part funny. Here are just a few examples from his speech:
"I have been most shamefully, most abominably treated... You have insisted on my entertaining you to an exceedingly expensive, not to say ostentatious, lunch... During that indigestible meal—I'm feeling the worse for it at this very moment—your behaviour and conversation attracted the unfavourable attention of everyone present. I feel I have been publicly disgraced."
Let's consider one more type of figurative language: the simile. We'll find a few of these:
[The valley] spread out from the Lion like a pool. It ran up the sides of the little hills like a wave.
Can you imagine a stretch of grassy land bubbling like water in a pot? For that is really the best description of what was happening. In all directions it was swelling into humps.
As you can see, a simile is a type of comparison, using the word "like" or "as," that helps you imagine what one thing is like by comparing it to something else. Above, for example, when the narrator compares the movement of the land to the bubbling of water in a pot, we understand very clearly what the bizarre movement of the land looks like in the story.