1.1. ThemeWe call the THEME (for) all elements related to the graphical layout of your site: pictures, fonts, colours... All files related to the theme are saved in a unique folder.
1.2. CssCSS (cascading style sheet) is used for all elements related to the style of your SITE. A font is a style, a color is a style, a font-size is a style... etc... A style is created using one (or more) file(-s) with .css as EXTENSION.
1.3. Bootstrap based themee107 is by default based on the bootstrap framework, so Jquery library is loaded by default too. The term bootstrap based theme means that, bootstrap is loaded into theme on frontend. The Admin area always uses bootstrap3 theme. How to create theme without jquery is not part of this tutorial. You can, of course, create a theme without bootstrap.
1.4. HeaderIn e107, the header is the part of your page BEFORE the main content (it can be on the top or/and the left part of the page). By default the header is the same for ALL pages on site. To use different header for some pages you need to use a workaround - see advanced section.