This is center aligned.
This is left aligned.
This is right aligned.
This is justified. This will fill the space exactly (except on the last line), even if it has to stretch a bit at times. Use wisely.
Why do I have a page completely dedicated to the text-align property? This might seem ridiculous, but this page is to help you understand when to use it's different values (left, center, etc.).
For a short while, I liked to align my paragraph text to center. Then I stopped. I stopped because I had learned that center text is in most cases a terrible practice, period. There are some exceptions to this. For example, you'll notice most of my pages have a centered headline, but paragraph text aligned to the left. Major headlines and sub headlines are usually an exception for center aligned text.
From a user experience point (or UX if you want to be professional), the human eye has a much easier time reading left aligned text vs. any other text. Users expect for text to start in the same position every time. With center text, each line starts at a different point, making your eyes stop reading for a few milliseconds to quickly find where the next line begins. This is not good.
As for right aligned text, the internet is not manga (yet) so avoid it unless there is a specific reason for using it (like a specific layout/template or something like that).
If you are interested, check out the article below by UX Movement. Now let's learn about the open graph!