In Todo mode each todo list is identified with a named category, so you can group together thematically related todo items. Each category is stored in a file, which thus provides a further level of organization. You can create as many todo files, and in each as many categories, as you want.
All todo files reside in a single directory, whose location is specified
by the user option todo-directory. This directory may also
contain other types of Todo files, which are discussed later
(see Todo Archive Mode and Todo Filtered Items Mode).
When you use a Todo mode command to create a todo file, the extension
‘.todo’ is automatically added to the base name you choose (as a
rule, this name is also used for the other types of Todo files, which
have their own extensions). As a user, you only have to deal with the
base name of a Todo file.
When you create a new todo file, you must also add at least one category
to it, and each todo item belongs to a category. It is not possible to
have an uncategorized todo list, but you can always make a catch-all
category with a generic name like “Todo”, which is in fact the default
name assigned to the first category when you create a new todo file, if
you don’t provide a different name; you can change the default by
customizing todo-initial-category.
The most basic level of organization is the todo item itself, since it contains the information about what you want to do. As detailed in subsequent sections of this manual, most Todo mode commands and user options concern ways of classifying and deploying this information by associating various kinds of metadata with it, e.g., the category it belongs to, its priority, whether it is to be included in the Emacs diary, date and time stamps, whether it is done or still to do.