Coding website

I know HTML and CSS but I think my coding knowledge is not that good. Maybe I can make something look ok, but I think I have a lot of mistakes. For example here is Website:
http://strata.alianceforum.com/h5-asdasdasdasd

It's done with minimal effort, nothing special, only added jQuery slider for banners but it's dumb to do. Anaway, what I want is someone to explain me how to code? How can my website work cross-browser? It seems like i code this main part wrong. I am not sure alos how to make two colum divs inside one div allready and also set border left for one of them so there is line separator. Can someone clear those problems for me? :)