ASK : I just want to ask to anyone who can help me, how to avoid duplicate content?. Thank you anyway...
Duplicate content is considered illegal in terms of Google, if its your content which you want to publish through different channels, then its not a problem. But if you copy some ones content and post it on your blog/website, then as recently what you may have noticed from the panda effect Google will consider you blog/website as a low quality website. Try avoiding copying, write in your own way.
Try to do some research on the topic you are going to write about to get used with the terminology(if you need to) first then start to write your post,article or whatever without consulting anything.Most of the time the result will be original and unique but if you are really worried about duplicate content just run a Copyscape search.
You can avoid the duplicate content by using copyscape.com which it gives a complete information of your site if it is duplicate or not. So that you can get a idea and try to make your content original. Google likes only the fresh conten