What is Duplicate Content?
Online Content that appears in more then one place.
How does Google handle Duplicate Content?
Google looks for Duplicate Content. When they find more then one page showing the same content they filter out all but one page and all the duplicate content will get shoved down toward the bottom of the rankings for that specific search and the main page they choose will stay in its appropriate rank.
For the most part Google does not treat duplicate content as spam. With that said if you do nothing but duplicate content they do reserve the right to view your entire website as spam and your website wont show up in searches.
Can I make a blog post and quote text from another website?
Yes. You can put a text in a quote. For example if your writing a blog post and you have your own original content, then a paragraph that in quotations quotes someone's text from another site. If possible leave a link back to the original website.
But if you are copying an entire article from someone website even if you put it in as a quote you will be dinged for that.