The first quotation, "What a shadow she threw on the wall with her slender body," is found in Chapter One of Ray Bradbury's novel, Fahrenheit 451. To find meaning in this quotation, it is important to refer to the entire sentence:
How immense a figure she was on the stage before him; what a shadow she threw on the wall with her slender body.
In context, Montag is referring to the the impact his first meeting with Clarisse, his new neighbor, has had on him. And although he tries to shake himself out of the sense that she is really an unusual and impactful person, he cannot lose the feeling that there is something strongly unique about her. He imagines her standing on a stage. When he refers to her as an immense figure, he is speaking metaphorically about the personal power she has, and then comparing that, literally, to the puzzlingly small shadow she "displays." How could someone so impressive, cast such a small, perhaps ordinary shadow?
If I were to paraphrase, I might write:
[For someone with such an impressive sense of self,] physically she appeared small and deceivingly fragile.
Your second quotation is also found in Chapter One. Montag has just come home, having met Clarisse. She is unusual in that she (and it would seem her family, as well) notices things that most folks do not. Instead of allowing the world to pass in a blur, Clarisse notices details.
If you showed a driver a green blur, Oh, yes! he'd say, that's grass. A pink blur! That's a rose garden!...
Clarisse's "details" are not unusual to the reader, but must be to Montag:
There's dew on the grass in the morning...And if you look...there's a man in the moon.
This kind of talk makes Montag nervous. They say good night and part ways, each going into his or her own house. Perhaps because Clarisse has brought to mind noticing the details of the world around one, Montag goes inside and stops to listen. He hears "...the electrical murmur of a hidden wasp snug in its special pink warm nest..." This probably refers to the noises made by the sleeping devices his wife is using—the electrical sound comes from their bedroom. Mildred, Montag's wife, listens to music each night in her Seashell ear thimbles, but does not close her eyes in sleep, as they are wired open.
To paraphrase, we need a subject, for the comparison of this metaphor. What Montag has heard is a hum...
...that is like an insect buzzing away in its nest, unaware of what is happening in the world outside his safe haven.
The metaphor gives the reader a sense of misgiving in that Bradbury chooses a wasp as the insect in its nest; this particular "bug" is capable of causing great pain when disturbed. This may be a description of Mildred. Or perhaps Bradbury is suggesting in this comparison, that Mildred's daily routine, completely condoned by society, is no threat to others as long as no one questions its presence or validity, and this may serve as foreshadowing for Montag's behavior later in the novel.