Custom WordPress theme

I need to create a wordpress theme that displays audio files of talks. These would be displayed in a grid of 4 columns and 3 rows. Visitors to the site then click on a talk that they like and listed to it. The site has been designed already. I just need the theme created. I have the audio plugins and all other details with me. I've attached a sketch of the layout so it is clear what I am looking for. Each audio file is a post. When a person clicks on a post it goes to a single page layout which I have designed already. See attached file. Pretty easy job if you know how to create a theme. I wish I knew how to.