HTML div ( newbie )

I have recently started learning html and css but I cant seem to figure out which approach is the best to get a certain task done .

I want to create a box at the top of the page that covers the whole screen from left to right at a certain height. And inside the box I'd like to have a text which properties can be controlled separately from the box .

So if have created 2 div and assigned 2 ID , one for the text and one for the box . And used CSS to modify the properties of each .

Am I working right so far ?