Formating

hr tag

The <hr>* tag (hr stands for "horizontal rule". It makes an HORIZONTAL LINE). The the red line above here. It's originally black but I applied some style (=CSS) to it in the head area of the HTML basic structure (but here, in this paragraph, the colors/style were modified in the middle of the paragraph (the so called "inline CSS" explained above.), using <span> 3 times).

br tag

The br tag breaks a line like now
(for whatever reason you may have), without being a paragraph. (after the word "now" there is a <br> tag)

del tag

The <del> tag marks a text as non-valid or deleted.

ins tag

The <ins> tag underlines the text to give the kind of enphasis s if he text has been filled in the blank space, or inserted.

Don't confuse this tag with the "u" one. "U" is not semantic. It just underlines and that's it, no meanings whatsoever.

small tag

This tag can be used in those small contract/agreement/purchase order/invoice letters.

The "big" tag is not used any longer. It works, thou. This task (enlarging) now is CSS business.

sup tag

The superscript tag is good to format things like 18²⁵+3, for instance.

sub tag

The subscript tag doesn't make it rain but can make the H₂O formula.

Bold and Italic

Here I make a bold word using the <strong> tag.

Better NEVER use the tag <b> to make bold. It's not semantic. This tag should be used to markup text as bold without conveying any extra importance, for example in article abstracts, where the beginning of an article is set in bold text.
(quackit.com).

And here's an italic word made with the <em> tag.

Avoid using the tag <i> for italic. It's not a much appropriate semantic element.