If I remember from my old high school American Literature classes correctly - and I probably don't - the difference between a metaphor and a simile is pretty straightforward in that a simile has "like" or "as" next to it, comparing two things, and a metaphor is simply a substitute for the actual thing in question.
Loose as a goose. Crazy like a fox. Two bad similes, but similes nonetheless.
I always fall back on the metaphor-rich poem "The Highwayman" when I scratch my brain for examples of metaphors: "The road was a ribbon of moonlight. The moon was a ghostly galleon tossed upon cloudy seas." Not "as" or "like" like similes - just a poetic substitute.
"I have fallen through a trapdoor of depression," said Mark, who was fond of theatrical metaphors. (An example from my dictionary.)
Some of my most favorite metaphors and similies escape into the air from the lines of the poetry of American poet Carl Sandburg: "... a voice like a north wind blowing over corn stubble in January." "Sunday night and the park policemen tell each other it is as dark as a stack of black cats on Lake Michigan..." And - my favorite, I think - "Mamie beat her head against the bars of a little Indiana town..."
I feel rather silly speaking of these things here, since there are several people who write and even teach these things for a living, who might pass by here and chuckle at my pained explanations. But remember, this blog is mostly me talking to myself, trying to interpret, trying to become clear.
Now, as to "allegory," I think it is much like metaphor except there is often a hidden meaning (or perhaps moral) that makes the reader think a bit about what the writer is really saying. Underlying meanings, sometimes, these allegories. And sometimes longer stories in themselves. For example, I think a lot of the old fairy tales are allegories of good vs. evil. Certainly Aesop's Fables are meant to suggest some moral. Jesus often spoke in parables, another form of allegory, meant to convey a complex subject in more simple terms. Poetry, of course, uses all these forms as tools of language, but usually in a shorter space.
All of this ties into poetry, the fun of poetry, the satisfaction of poetry; and I intend to learn more about it. If not to actually write it, at least to be better informed so as to enjoy it more.
