To utilize is to use what you have or what's available, and it's a three-syllable word meaning the same thing as the one-syllable "use."
The word utilize is often a more formal way to express "putting something to use." If you don’t have time to go to the store but you need to come up with a science project, you might utilize what's already in the kitchen. Most of the time you can use the verb use as a synonym for utilize. You can utilize a shorter word to make a sentence easier to read.