Widgets are little bits of code that you put into "containers" to add something to your web pages. You can add, remove and reorder widgets from the Blog settings->Widgets tab in the admin interface.
Each container appears in a specific place in a template, typically the header area, sidebar, and footer area are containers. If you change your blog template, the new template may not use the same containers as the previous one. Make sure you place your widgets in containers that exist in the specific template you are using.
Your template may or may not have widgets pre-selected by the template author. If it does not, then $s will provide widgets ... if the template has containers with names it expects. Widgets can also be "hard-coded" into your template, meaning no container is used. Blog A header is an example of this: the title and long description are coded widgets.
This is the first post, which makes it show up last in the posts list. It appears in multiple categories and has 2 comments.
Each post (or "item") must be in a primary category, and can also have additional "sub-categories". There is no limit to how many categories a post can be attached to. It is also possible to configure Quam Plures to allow posts to be attached to categories in different blogs.
The first comment has been published (approved), and the second is in draft (moderation). Log in to see and approve or delete the second comment. By the way both of these comments are impossible given the default configuration: anonymous comments are not enabled. They are here only to show you about comments in Quam Plures.
Technically each post is attached to a category which is attached to a blog, instead of the post being directly tied to a blog. That may be a small internal detail, but it causes confusion so there you go!