Navigate to the Roots theme home page at http://roots.io/.

You might take some time to familiarize yourself with the resources here. (It's a great and growing development community.)

Proceed on to the GitHub project by clicking on the GitHub link. The direct URL is https://github.com/roots/roots.

Download the ZIP file.

Extract it.

Rename the extracted folder to your desired theme name as shown in the following screenshot:

Navigate inside the main theme folder to the style.css file as shown in the following screenshot, and open it in your editor:

Once you've opened the file, you'll notice that it contains no actual styles. Site styles are provided by a stylesheet css folder located inside the assets folder, which is compiled by Bootstrap. We'll follow this approach as well. The style.css file then serves primarily to name our theme, give appropriate credits, declare the license, and so on. So, let's do that...