WordPress themes allow users to customize the design, layout, and presentation of their blog. Themes can be customized using templates, images, style sheets, and code. WordPress supports common file formats like GIF, JPG, CSS, and PHP. Users can manage and preview themes from the admin dashboard before uploading them. Default themes are available on the WordPress site. WordPress draws information from a MySQL database to generate HTML code for personalized web pages. Themes consist of a header, content section, and footer to display site details, navigation, pages, and copyright information.