How to "Center" things in html.

Often times when building a website, something gets installed and it is aligned to the LEFT. (Like the Amazon ad I placed below right)

I like to have things centered, so many times I have to add the following html code in order to make that happen. - (There are a few times when it doesn't work, like maybe with HTML5 - but 9 out of 10 times it will work.)
 
Now, you have to do this in the "text" editor (On Blogger, it;s the HTML editor)  not the wysiwyg (Or Compose) editor., but, here it is:

<center> PUT YOUR TEXT, IMAGE OR OTHER STUFF HERE - THEN PUT CLOSING TAG </center>

That's all there is to it.