I need some really great advice.
I am an experienced JavaScript and PHP programmer and am used to writing and deploying standards-based html/css  and scripts written from scratch.

BUT, I am not used to frameworks or content management systems whatsoever. Please help.

MonoX CMS is easy to use without knowing much, but I like and need to understand the code.
I am choosing MonoX, to build a classifieds site, due to it's amount of built-in features, and particularly the ways you can "connect" different modules. The social networking related features are very attractive as well. It would take me months to script all that functionality, and tons of API reading and research-So why re-invent the wheel? I choose MonoX.

Please help. What I need is some good advice to streamline my knowledge from beginner to intermediate within a few days.
It could take a lot of reading and time to find some key gems of information that I need. A good start would be how I can use CSS and where to put the file, I mean is that even possible? My main question is how can I best adapt HTML/CSS/JavaScript knowledge to this CMS ?  Can anyone help, quickly? Thanks