Snippets are short templated messages that you can save, which makes things more efficient for messages you might want to reuse.
Snippets are shared across all Users in your account.
At the bottom of the message composition box view is the icon for Snippets, which looks like this:
When you click that icon, you'll see options to either:
Add a new snippet. When adding a new snippet, you enter a name for your snippet, a keyboard shortcut, and the actual content of the snippet itself.
Select and insert an existing snippet. This will insert the templated message wherever your cursor is in the message box.
Delete a snippet. Click the X next to any snippet to delete it.