Bold, italicized, underlined, strikethrough, superscript, and subscript are text styles that you can apply individually to text. Although they are different tools, they can all be applied in the same manner.
First place the cursor where you are going to start typing.
Next, go up to the desired style button(s), and click on it.
Any text you type from there on will have the selected style(s) applied to it.
First, select the text whose style you wish to change.
Next, go up to the desired style button(s), and click on it.
The selected text will reflect the chosen style.