Use your gradient
Choose the start and end colours. Linear blends across a direction; radial blends out from the centre. For a linear gradient, change the angle to turn the direction.
Copy the CSS rule and paste it inside the selector for the element you want to style, such as the body or a banner. In a website builder, use its custom CSS area if it has one.
The output is CSS code, not a downloaded image. Check that any text placed over the gradient remains easy to read at both ends.