1. Open up the Webflow Designer.
2. Click on that '+' icon to toss in a new element.
3. Pick 'Section' and drag it right onto the canvas.

1. Select the section you just added.
2. In the 'Styles' panel on the right, set the height to cover the viewport. For example, set the height to 100vh.

1. With the section still selected, head over to the 'Background' settings in the 'Styles' panel.
2. Click on 'Image & Gradient' and then click on 'Choose Image'.
3. Select or upload the background image you want.

1. In the same 'Background' settings, use the dropdown menu next to your image to set the 'Position' to 'Fixed'.
2. Make sure the 'Repeat' option is set to 'No Repeat'.
3. Set the 'Size' to 'Cover' so the image covers the entire section.

1. Switch to 'Preview Mode' or publish the site.
2. Scroll up and down to see the fixed background effect in action. The background should stay put while other content moves.

1. To make it look even better, add more content sections under the section with the fixed background.
2. Use different elements like text, images, and videos in these sections to see how the fixed background interacts.

1. Go back to 'Designer' mode.
2. Make any necessary tweaks to the image positioning, size, or section height to get the visual effect you want.
3. Ensure the site is responsive by testing it on different screen sizes.

By following these steps, you can create a cool fixed background effect in Webflow.