The template list shows every page layout available to your site: Sprwt's built-in templates for pages, any (Client Custom) templates built for your business by Sprwt, and DIY.

• A fixed template renders a predefined layout; in the editor you only see the options the template exposes (grouped under Global Page Options or the template's own sections).
• DIY starts empty and lets you stack any modules from the module gallery in any order, edit each one, duplicate, move up/down and delete them. DIY is pre-selected for new pages and is what most sites use.

Blog posts get their own list (the Blog Post Template plus DIY). You can change the template later from the page editor's Settings > Template > Change, but options entered for the old template are not carried over to the new one.