1. Click the Settings Icon 
in the top right corner of your Outlook Web app.
2. Click on View All Outlook Settings located at the bottom of the Quick Settings Menu.
3. When the full Settings menu opens, click Mail, then Compose and Reply.
4. If you have previously created a signature, it will display in the text box area.
5. To create a new signature, click + New Signature, enter a signature name, create your signature, then click Save in the bottom right corner of the Compose and Reply window.
6. Next, set the default signature settings for your account.
Visit the Outlook: Getting Started article to learn more about using Microsoft Outlook.