When you talk about the opacity of something you talk about how see through (or opaque) it is, or how much light it lets through.
For CSS purposes, something whose opacity is 1.0 is not see through at all, and something with an opacity of 0.0 is completely see through (you wouldn't notice that it's there.
For this assignment you need to create a new webpage.
You will also need an image.
In the body of your page, put in your image (don't forget to include its class).
Load your HTML file into your browser.
Your page looks a little washed out, doesn't it?
Change the opacity level in your style section to 1.0, save it, and then reload your page. Then change it to 0.0. How does your image change?
Fix the position of the image, and give it an opacity of about 0.3.
Create a heading for the page.
Create text based content for the page, enough so that the text can be seen to scroll while the background image does not.