I am not very good with CSS, HTML and mark-up, but after having read many and many CSS articles, I just have no idea how to get the div-elements on the right place.
I would like to have the right-menu and content in the right place. If you have general comments regarding the current state of my HTML and CSS, please feel free. I have worked with CSS, HTML much, but never built a site from scratch with div-elements.
Looks like a simple 3 div layout. You need to create 3 divs. One for the left, middle, and right-hand content. These three divs will be placed in a wrapper div.
So take your left_menu, content, and right_menu divs, give them a width and set them to float: left; so they will all be placed beside each other. Place them inside a wrapper div that is larger than all three. You're done!