Words with more than one syllable are spoken with a stress on one of the syllables. This is important for correct pronunciation as well as for using the word correctly. For example, one definition of the word "subject," when pronounced SUB-ject, is a topic of discussion. If the stress falls on the last syllable, as in sub-JECT, then the word becomes a verb, meaning to cause someone to suffer.
It is important for those learning English as a foreign language to be aware of how a stress on the wrong syllable of a word can obscure its meaning. The word “handle” for instance is pronounced HAN-dle, and the word “motel” is pronounced mo-TELL. However someone new to the English language could easily switch these stresses, pronouncing them MO-tle and han-DELL. These words are not recognizable to the native English speaker and could easily cause misunderstanding in conversation.
When a particular word in a sentence is emphasized when spoken or printed in bold or italics, the meaning of the sentence changes. For example, look at the sentence "Karen doesn't think George wants to go to college." The meaning of this sentence is simple when you first read it. But if certain words are stressed in the sentence, the meaning either changes or we gain some new information.
An example of change in meaning due to word stress might be: “Karen doesn't think GEORGE wants to go to college.” The stress on “George” then becomes a clarification -- someone might want to go to college, but not George. “Karen doesn't think George WANTS to go to college” tells us that George has considered college, but doesn’t like the idea. “Karen doesn't think George wants to go to COLLEGE” indicates that George may have plans, but not a plan to attend college.