Like say I have a blog and I read some news on Yahoo! or various other websites such as Engadget, and I go and create a post about a particular article and of course, not writing the article verbatim but kinda paraphrasing it and then also linking back to the site, is this okay to do? Also, if I give my opinion on the matter and also link back to the original article, is that okay? I'm mainly concerned about the legalities and the ethical stance of doing this. I do see that often times the Endgadget guys will post a link to Joystiq with their opinion on the matter/article. I'm guessing it should be okay for me to do it then.
Copying an entire article or substantial part of an article would violate the copyrights of the article's owner. The best way to deal with this issue is to summarize the article in your own words and then link to the original article. Alternatively using only a couple of sentences from the original article as a description/teaser and linking to the article would be okay as well. Using more than a brief section of the article as a description (like the length Google uses) risks you running afowl of the article's owner and DMCA actions being taken against you.
Spelling correction: Fair use Here is a vary authoritative page on fair use: http://chillingeffects.org/fairuse/
If you really want to understand fair use, read case law. Reading the codified law only gives you a very small aspect and understanding of what you can and can't do. Your best bet is to talk about your thoughts on the article without going over it and link to the article.