How to Start Implementing Own Design

I’m getting a quite frustrated with WordPress. I am a web designer new to WordPress. I’m not a novice with HTML and CSS and I understand how the themes basically work but I can’t find any help on getting started with implementing my own design to make a theme.

I have a design I already did and I just want to get it to work in WordPress. When I look around the WordPress docs for design & layout all I find is very specific things like developing a color scheme and designing a header. I thought I found the right thing for me when I found the header “Which files do I modify when I start to design my site?” but that just directed me back to the Design & Layout section. Should I just find a theme that is a bit similar and start messing with that to make my own or is there some other way to start? Maybe some blank template?

Thanks,
~peter