There are four primary buttons in the Visual Editor ToolBar that allow you to control the basic formatting of text in your posts:

Sets selected text  as bold.

HTML view: <strong>Bolded Text</strong>

Sets selected text as italicized.

HTML View: <em>Italicized Text</em>

Sets selected text as strike-through.

HTML View: <span style="text-decoration: line-through;">Strike Through Text</span>

Sets selected text as underlined. This button is located on the second row of the visual editor toolbar, accessed by clicking the “Kitchen Sink” button.

HTML View: <span style="text-decoration: underline;">underlined</span>