i am still a little confused

You can write about anything you like... as long as it is in your own words with your own ideas. Copyright comes from the word "copy". That mean that you cannot copy anything written by someone else. If you re-write someone else story in your own words... while essentially saying the same thing without bringing anything new to the article... it is plagiarism. If you want to write an article about someone's work or discovery in medecine... you should publish the name of the person who made that discovery as a recognition of its work when you publish its facts. If you write a biography... you need to make sure that what you are saying is true... otherwise you could be sue for defamation. You can also be sue if you insult that person or reveal some private information about that person.

Only if you try and pass it off as your own work. You will have to refernce any books or articles that you get information from, but as long as you do that correctly you will be fine