Strong is used to indicate strong importance

This text has added emphasis

The b element is stylistically different text from normal text, without any special importance

The i element is text that is set off from the normal text

This text has a strikethrough

Superscript^®

Subscript for things like H₂O

This small text is small for for fine print etc

Abbreviation: HTML

This text is a short inline quotation

This is a citation

The dfn element indicates a definition

The mark element indicates a highlight