How do I make text bold in HTML?

use <strong> or <b> tag

also, you can try with css <span style="font-weight:bold">text</span>

The Markup Way:

<strong>I'm Bold!</strong> and <b>I'm Bold Too!</b>

The Styling Way:

.bold {
  font-weight:bold;
}

<span class="bold">I'm Bold!</span>

From: http://www.december.com/html/x1/

<b>

This element encloses text which should be rendered by the browser as boldface. Because the meaning of the B element defines the appearance of the content it encloses, this element is considered a "physical" markup element. As such, it doesn't convey the meaning of a semantic markup element such as strong.

<strong>

Description This element brackets text which should be strongly emphasized. Stronger than the em element.

HTML doesn't have a <bold> tag, instead you would have to use <b>. Note however, that using <b> is discouraged in favor of CSS for a while now. You would be better off using CSS to achieve that.

The <strong> tag is a semantic element for strong emphasis which defaults to bold.