In the themes directory, create a new directory named c5book, but any other name is fine as long as you're using letters and underscores and avoid the special characters available on your keyboard.

Create a thumbnail 120 x 90 pixels of your site and save it as thumbnail.png within your theme directory.

Create a file named description.txt in the new directory by using a text editor, such as Notepad.

Open the file and enter the name of the theme in the first line and the description on the second line. Its content should look like the following:

c5book Theme
Concrete5 Theme by Remo Laubacher

Save and close the file. You should have a structure like the one shown in the following screenshot:

As we're going to create several page layouts sharing the same header and footer, let's create a directory named elements for these common files.

Within elements, create a file named header.php and insert all the preceding HTML...