What is stress, why is it important, and what are the levels of stress? (Linguistics)

Stress in linguistics is the emphasis that is given to a particular word or syllable. This emphasis can be lexical or syntactic. English has variations in stress that contribute to the complexity of the language.
Patterns of stress produce various effects upon the listener. They can provide emphasis upon certain words and contrasts or focus with respect to meaning. For example, the difference between the pronunciation of the phrase "the white house" and "the White House" indicate that one phrase is simply describing a house that is white in color, while the other is the residence of the President of the United States. Lexical stress involves the difference in meaning of a word. When the stress is placed upon a given syllable, a word can mean one thing, while it can means something else if the stress is placed upon a different syllable. For example, depending on the pronunciation of the noun August and the adjective august, the distinction between the two words is made to a listener. Even with words that are spelled differently, the meaning is conveyed by the stress given to them. For instance, without seeing these words, the listener can distinguish the lexical difference between insight and incite.
In English, there is what is also called variable stress. Different regional dialects, for instance, place stress upon certain syllables in words. For example, in the Deep South, the name Monroe is pronounced with the stress upon the first syllable, whereas in the Middle American dialect, the stress is on the second syllable. Stress placed upon words in sentences is called sentence stress or prosodic stress. This type of stress involves phrasal stress or contrastive stress. Phrasal stress, for instance, involves stress which extends the word stress upwards by at least two levels. Again, regional dialects are often indicated by this other type of stress. For instance, in contrast to Middle American dialect, a Southern dialect often ends a sentence on an upward tone.
http://gordon.faculty.linguistics.ucsb.edu/Gordon_2010_Stresssystems.pdf

http://pachamamatrust.org/f2/1_K/commerce/Intro/002b_Stress_KCoA.htm