Figurative language is something you use when you want to exaggerate or describe something with detail. You might use figurative language if you write poetry, or if you want to explain something that's really important to you. If you want to compare something to something else, or explain something with feeling, you would use figurative language in your description of that thing. If you want the person you're talking to to really feel your feelings, figurative language can be very useful.
A simile is a commonly-used form of figurative language. You use a simile to compare one thing to another thing, using the word "like" or "as" in between. For instance, you might say that your girlfriend is as beautiful as a rose or your sister's backside is as big as a bus.
Metaphors also make comparisons, but without using "like" or "as." For a metaphor, you simply say that one thing is another; in a classic line from Romeo and Juliet, Shakespeare wrote, "Juliet is the sun" (famousquotes.me.uk). She was not really the sun, of course, but from Romeo's perspective seeing Juliet's face in her bedroom window was like seeing the light of the sun shine down on him.
Imagery is when a speaker or a writer describes something so well that you feel like you can see it, hear it, taste it or touch it for yourself. In other words, imagery is an extremely detailed sensory description. Poems might use imagery to describe a sunset or an ocean shore in great detail so that the reader can picture that image in their minds.
Idioms are types of figurative language that appear in everyday conversation. Your mother might tell you to "put a lid on it;" she means that she wants you to be quiet. Even though she says something strange, you understand her idiom and what it really means.
Hyperbole is a drastic exaggeration. This type of figurative language is also common in everyday language. A child might complain that it has taken his mother 100 years to finish the grocery shopping so they can get a treat; a teenager might exclaim that his math teacher has assigned him 2,000 problems to finish over the weekend. Neither of these statements is true; they are used to show the way the speaker feels about the situation by using a big exaggeration.
Alliteration and Onomatopoeia
Alliteration is the regular repetition of a consonant sound. The tongue twister, "Peter Piper picked a peck of pickled peppers," is an example of alliteration. Alliteration adds rhythm and an almost musical quality to your words. Another sound-related example of figurative language is onomatopoeia. Onomatopoeia is a device writers use when they write out the sound something makes. So for instance, the words "buzz," "whoosh" and "plop" are all example of onomatopoeia.
Personification happens when you give human-like qualities to non-human things. For instance, a talking pig in a cartoon show is an example of personification. Another example might be to say that a storm attacked a ship with intentional force. The storm has no will of its own, of course, but the person describing it has given it a human personality.