For centering, define a div container with a width and use a margin:
margin: 0 auto;
Then in body:
This div container will be centered on page or, if used inside another container, centered inside it.
For the fonr tags, use <span></span> tags.
Use CSS to set underline or any other text decoration. Best to use one external CSS file to control layout of your pages. Next best is to use embedded CSS where you put the styling between style tags which must be place between the head tags. Next, if you only need to style a tag or two on just one or two page, use inline styling where you stle within the opening tag with the style=”” attribute.
There’s a lot more, but should get you started. See the w3c.org site for the standards: