after I make my workspace, how could I say that it is correct?

You should be able to down load the files for each lesson, this will allow you to compare your CSS to your instructor's as well as add your CSS to the html file already completed so you can preview your work. in the upper right corner there is an eye symbol that when selected you can preview your work.

if you are in doubt about whether your code is correct you can always post it here, either by using the mark down cheat sheet or taking a snap shot of your work directly from work space, and some one can look it over for you.

Finally there are sites you can go to that will check your code for errors. This just checks for syntax errors, it won't tell you if you are doing everything correct but it useful as a final check. Most use Chrome's dev tools. Nick walks you through how to do this in the how to make a web site course, if you've taken this course review the video "use developer tool" in last section "debugging html and css problems". If you haven't taken this course, go to the library, select html, select how to make a website, select debugging html and css, select use developer tools.

Hope this helps!