Using material from outside sources is a good and important part of research; however, you must cite and quote the source material, otherwise it is considered plagiarism, even if it is not intentional.
Quoting means placing the outside source material in quotation marks. " "
Citing means telling the reader who wrote this material and where you read it.
Then you are supposed to write your own analysis of the material, using your own words and original thoughts.
Using an essay you found on the internet, changing a few words here and there, and turning it in as your own work is not a good idea.
Most of the "academic" essays on websites are horribly written. They may have some fancy words, but usually there is no substance to what they are saying, and often they make no sense whatsoever.
Trust me, your own writing is better.
Example:
"The sharpest contrast I see between Van Gogh and Picasso is the impact they had on the world around them. Viewing these artists in context, in their own generations, is extremely important when asking who made the greatest mark on modern art. Van Gogh was the stereotypical troubled artist who used his paintings to describe how he felt. Those around him never quite grasped his greatness; perhaps they knew something we do not. Picasso made an immediate impact on the people he lived with, and that is the greatest sign in determining who was the most influential.
People follow leaders, those who stick their necks out to head the charge. Modern art, while taking note of the expressionism of both artists, followed Picasso; this is evident in the novel forms of today's artwork. Art is no longer simply eye candy, but rather a medium for an artist's communication. Modern art has something to say, and if we are to follow the path it treads, we had better listen."
The above may sound good to you, but really read it and think about what it means (or doesn't mean). Its