How do I use <meta and its outputs?

Answer 1

The HTML <meta> tag is used in situations where you want your website to be registered in a webcrawler index or have the accessability option for the accessable-blind. (WAI-ARIA)

In basic, <meta> is the metaworld information not really used by Your page, but by the Browser or Page readers.
<meta charset="UTF-8"></meta>
<meta name="viewport" content="width=device-width, initial-scale=1">

The charset or viewport is used by the Browser to tranceive information / adjust the scale of the page to fit on your screen.
The meta attributes above are some of many - which define some hidden but important information, so you need not mind. :)

Answer 2

Thanks