First Things First
Choose a good internet browser. This is just my personal preference, but I'm liking Chrome more and more. I still use Firefox a lot, but Chrome seems to have a little bit better add-on for learning and debugging CSS.
I started out creating webpages and viewing them in Internet Explorer. That was horrible. The best way is to make it work in a browser that interprets CSS properly. This isn't my opinion, it's just a fact that Internet Explorer doesn't show things properly.
Once you get the site or webpage the way you want it in Firefox or Chrome, then you can go to Internet Explorer and see what things you need to fix. You can then make a CSS file that is specific for Internet Explorer.
The Real Star
Although the browsers Chrome and Firefox are great, the real star for debugging or learning CSS is the add-on. These add-ons, for each browser, are called Developer Tools. Firefox has one you can install called Firebug. Chrome has one that is built in. Internet Explorer has one, but it's really clunky and glitchy.
If you have to, Internet Explorer: