Getting savvy

You'll no doubt have noticed a different look for the site. I've been playing with the HTML coding and figured out a few things; things I wanted to change that have bugged me since I went to a nice, large monitor. So, I fixed those things but now I want to do some more design work and I don't know how to do it. So, for those of you who do, I'm looking for your help to get started. I want to start with the header, you know, the part where the title sits. I want to put some cool, colourful graphics in there - either something I design myself or something I steal from somewhere else. So, how to I get it up there? Can I do it through the new blogger or do I have to do it through the HTML code? And if in HTML code, how do I do it? Help please!