Outlines in Word 2013 have several levels. Beneath topics are subtopics, and those subtopics can have their own subtopics. For example, your main topic may be Things I Regret, and the subtopics would be what those things actually are.
To create a subtopic, simply type at the main topic level, but don't press Enter when you're done. Instead, click the Demote command button, found in the Outlining tab’s Outline Tools group and shown in the margin.
The keyboard shortcut to demote a topic is Alt+Shift+→.
Demoting a topic has these effects in Outline mode:
The topic is shifted one notch to the right in the outline.
The paragraph style changes to the next-highest-numbered heading style, such as from Heading 1 to Heading 2.
The Level item in the Outline Tools group changes to reflect the new topic level.
The parent topic’s circle grows a plus-sign (+) symbol. It’s the sign that subtopics exist or that the topic can be expanded.
You can continue creating subtopics by typing them and then pressing the Enter key at the end of each subtopic. Word keeps giving you subtopics, one for each press of the Enter key.
You don’t really create subtopics in Word as much as you demote main topics.
You can also use the Level drop-down list, found on the Outlining tab, to instantly promote or demote the topic to any specific level in the outline.
Unlike when you’re creating main topics, you can get a little wordy with your subtopics. After all, the idea here is to expand on the main topic.
According to Those Who Know Such Things, there must be at least two subtopics for them to qualify as subtopics. When you have only one subtopic, either you have a second main topic or you’ve created a text topic.