how to add a background image?

Answer 1

You need CSS for that. For example, to add a background image to your body element:
body {
background-image: url("myimage.jpg");
}

You can add the background-image CSS property to almost any HTML block element, such as divs, tables, paragraphs, etc.

Answer 2

CSS, does that go with Html?

Answer 3

write background-image on body{}